I may have a gig recording a solo piano,  the only condenser mics I have two of is pair of AKG Perception 170
 
I have a Neumann TLM 193 and a 103
a Rodes NTG 3 shotgun mic,  a Shure SM81
 
I don't mind buying as long as the mics are useful for other things.... 
so expanding the palette in a way that will also serve well on a Piano is the advice I'm seeking.

What kind of music?  The options are quite vast.  
 
To get the ball rolling.  For Classical, the most popular piano mics are the DPA 4006, the Schoeps MK2, and the Neumann M50.  All small diaphragm omnis used in a spaced pair.  I use a Josephson C617set pair for mains and Sennheiser MKH8040's or TLM 107's for spot mics.  A common approach is to use 3 pairs of mics.  A slightly distant pair on tall stands in front, spaced a few feet apart, a "main" pair slightly forward off the tail of the piano a few feet back, and a couple spots wherever you want to stick them.  
 
For pop music, the AKG C414, the AT4050, and any Neumann large diaphragm mics are classic.  The TLM193 is a great mic, basically a cardioid version of the 170, and would work well if you had a second one.  
 
A good, open sounding stereo ribbon is also fantastic like the AEA R88 if you like mellow.  

FWIW, here's a screen capture of the mic'ing of the grand piano in Addictive Keys.
 

So much depends on your situation. I have never mic'd one myself, but have read different variations with the top opened which a condenser should capture. An interesting tid bit I caught was a guy who used a piezoelectric mic (rather cheap) to also record a channel of the body resonance inside the body (I *believe* he said he mounted it directly to the soundboard with a temporary adhesive, but do not recall "what" now). Attaching such a mic is far more critical than using one though; that "adhesive" is a big deal for such a thing.

Daniel, Thanks for the serious input!
Mr Maartian, thanks for the laugh. And Mettelus, I probably shouldn't bring the construction adhesive.
 
To start with I just got a pair of Audix scx25a off ebay for the price of one.  Though I've never used an Omni mic I can see in my mind how a pair of those would be ideal. I'll be looking for something more affordable, maybe I'll get lucky again.
 
As for style, he wants to go through a number of styles.. making a demo of his playing essentially.  I can see the options are vast, but I think the fun will be vast as well.
 
Any thoughts on those Audix mics I grabbed?

I can't play piano, but if I had cash coming out of my ears, I would have one for sure 
 
Just sayin LOL
 
As for mic'ing one up, I'd have used a pair of condenser mics... So don't listen to me haha
 
That picture posted by The Maartian almost made me laugh out loud 

This is a great resource from Shure. It explains different mic types, how to choose them, and how to use them for different instruments.  Includes a section on recording pianos.

Thanks Karyn, I agree this is a great resource.

synkrotron
That picture posted by The Maartian almost made me laugh out loud 

I like the way your lips move when you say "overkill". 

TheMaartian
I like the way your lips move when you say "overkill". 

Dammit! I didn't think you'd notice