I'm in Australia so I thought maybe the new M3's might be a good choice but if anyone's had good results with another pair I'd really like to hear from them. Also best techniques for an upright acoustic piano, I've always had trouble getting a really good sound when I record piano, no problem with anything else.

Most of the sound of the upright is at the back. I use a Rode Classic top of the line LDC condenser there in that position. It is also nice to take the front cover off and mic the front hammers with either a signle SDC or a pair of them at the front. You get a little more percussion effect at the front. Usually there are no phase issues either.
 
Make sure it is nicely tuned. Even a slightly out of tune upright sounds bad to me anyway.
 
When you put the mic at the back if there are other things going on you need to drape over a heavy doona or something and block any outside sound out otherwise it tends to pick that up too. I move the piano out from a wall to form a large 45 degree angle. Then I slide a soft baffle in there against the wall to get rid of the hard surface. Then with the baffle there and the top of the piano you can secure a heavy something over the whole thing to isolate the rear mic a bit more.
 
Good luck.
 
 

Thanks Jeff, I've been using a Rode LDC on the open top, and a pair of dynamic mics at the open front. I've also tried close to the strings and bringing them back various distances till they're level with the ears of the pianist. I will try a pair of close SDCs at the front, I think you're right they will catch more of the percussion of the hammers and give it a bit more brightness. I do like the sound of two mics at the front and I think my decision to go with dynamics has been holding the sound back.
I hadn't thought about moving the piano out from the wall and miking the back, great idea, I'll definitely give that a go and try your suggestions re baffles and angles.

For what genre.  Jazz, classical, pop?
 
The techniques will all be different. 
 
For jazz there is usually a stereo pair near the curve, just outside of the piano.  Rode is fine, though ribbons and high quality cardioid condensers are popular.
 
For classical, it is traditional to mic several feet away from the piano with AB omnis, not directly in front, but toward the tail.  The height is determined by following the lid plane to avoid nasty reflections.  DPA, Schoeps, etc are the best microphones for this technique.  (best to try in a big room only)
 
For a harsher, clunkier pop sound, you usually see 2 microphones a few inches above the strings, usually near the hammers.  C414's are popular for this.  Omni pattern is good to avoid too much proximity effect.

Many thanks Daniel, mostly jazz, modern pop rock and ballad styles. Classical is played often but not recorded much. This is an upright I'm recording, not a grand though. I'm leaning toward the SDC pair close to the strings in front, interesting about the Omni pattern to reduce proximity effect (Rode NT55's? as I was considering the M5's but they are only cardioid, and about $400 a pair cheaper), maybe just a little further back?
I will try Jeff's approach of back miking using a LDC as I think this might help reduce extraneous noises as well as giving me the LDC sound. Then mix all three tracks to taste. I guess this will vary depending on the type of music as you said, and also whether the song is piano solo and vocals, or there are other instruments involved.
I've not any experience with ribbon mics, can you give me an idea of what they will bring to the recording?
I guess I'm still trying to decide which mics to buy, I'm getting some good ideas here so thanks again.

best results I've achieved thus far (and please keep in mind this is my piano, my room, and most important, my ears<G>!)... a pair of Earthworks SR77 small capsule cardiod condensor microphones placed at the same height as the top of the piano, about 3 feet from the piano, aimed down 15 -30 degrees and spaced as a coincident pair. The wall behind the piano was about 8 feet from the piano, and I ended up hanging a couple of very heavy moving blankets on stands about a foot from the wall covering about 2/3 - 3/4 of the wall surface. I then added a Royer SF-12 stereo ribbon microphone about 4 feet from the floor and about 2 feet behind the piano player. The ribbon ended up being the primary track, with enough of the Earthworks tracks to add some detail. If I could do that particular recording over again I think I might try cheating the Earthworks microphones closer - but at the time I really expected them to be the main tracks, and I wanted some room in them.

I do not record upright pianos often because, well, because I don't have one<G>. This particular piano happens to sound really nice, as I type this I think I need to make arrangements to record it again.

FWIW, I use the same three (four??) microphones to record my Yamaha baby grand, the ribbon stays behind the player, and the condensors go under the raised lid, spaced towards the edges of the piano, and maybe a foot back from the hammers. The piano lives in our living room, which is not an ideal recording space, and it isn't really placed optimally (but then the wife seems to think the primary use of the living room is living, not recording - go figure). Nonetheless, I have managed to get a couple of piano tracks that I really like,

Right now the poor piano is in desperate need of some attention from a local piano tech, but when I get around to that I'll have to post a track with this microphone setup. I should probably note that this results in a somewhat forward piano track - this ain't Bill Evans or even Liz Story... but I bet if I backed off on the condensors I could get something close to that.

Now if money were no object I would absolutely install the Earthworks PianoMic system in the piano. If you have not had a chance to listen to it you probably ought to - although you will want to lock your credit cards away before you do<G>!
 

What many are forgetting is the whole of the back of the piano is a giant sounding board and more sound still emanates from there than anywhere else so it is an area that should not be ignored. Trouble is most have not tried it so they don't know how good it can sound.
 
All of the advice above is good for front on recordings but if you only had one decent microphone then the back is the best place for it. As I mentioned I also put the mics out the front too to capture a little more detail but often I have found the back sound is the one I run with a lot of the time.
 
Also a lot of the techniques mentioned with front on recordings are not great if drums are in the room for example. You will get terrible spill from the drums there. Everyone is assuming you are over dubbing which maybe not the case. (especially in a Jazz situation) The great thing about the back recording is you can cover the whole area in and create quite a nice space inside that results in a lot of less spill coming in from other areas.

I wasn't forgetting anything... the cardiod pair I described is aimed at the sound board - I guess I just assumed everyone would "know" that. My bad.

I've never liked the effect of covering the space behind the piano (and the microphones), but I think that is just personal taste.

The only comment I'd debate is the comment on leakage or spill. If this is a jazz setting, with the entire ensemble playing together, well then I WANT the spill. But again, that is just personal taste.

My argument would be that folks ought to try it, sometimes it's not nearly as scary as it might sound.

One last thing - I almost always have a microphone picking up from the players perspective... that's what the player is hearing. For acoustic guitar I'll place a microphone at ear level just behind the player. For piano I've tried a similar position, but usually find that I want a little more distance - and, no, I have no idea why it works that way for me.

I'll also concede that if one has only one decent microphone one's options are limited. I think I also make the mistake of assuming that everyone has several microphones. My own locker is still pretty humble, but I guess it is not entirely representative?

I agree Bill about recording spill but it sort of depends on how loud the drummer is. I have just recently recorded a trio with upright piano, an electric bass player and my son playing drums. They were doing a fairly loud rocky sort of groove and I found the front mics although nice from the piano point of view ruined the drum sound a bit too much (added a little too much room for my taste) and I was very glad I had the rear sound as an alternative. The front mics also picked up a little too much bass sound (coming from a small amp but it was very much there) and it too ruined the direct bass sound a bit. Quite a different situation from quieter drums and double bass for example.
 
The moral of the story is (and this is the most important advice!) is you cannot really determine the best micing arrangements until the band is in position and you have heard them playing the tune. You can be prepared of course but you also need to switch your thinking and do things differently once you hear this.
 
An upright Jazz piano trio could mean a loud piano player, a soft drummer playing brushes and a double bass player but it can also mean what I experienced too, a not so loud piano player, quite a loud drummer and an electric bass player. Worlds apart, different approach for both of those situations. Let the music dictate what the best thing to do is. Also no amount of them telling you what it is going to be like will replace actually hearing them do it.
 
 

Sorry, I missed the upright bit.  Yeah the back is a good place.  Some attenuated highs but nice and smooth for jazz. I have also had good results removing the bottom panel and placing two omnis on either side of the legs.  This is assuming pedal noise is not an issue.