I am happy with the electric and acoustic basses of IK SampleTank 3 and one day I will grab Mondo (when it is less than $100). Before I got ST3 I was considering very decent B-BassV  -  you may check it here    http://www.chocolateaudio.com/products/b-bassv

Also Craig Anderton collection of Gibson EB5 bass is IMO great too. It should still be available at Cakewalk Store.

This is what I've been defaulting to lately. Pretty happy with the results
 
Electric = Modo
Upright = Trillian
 
I'm a big fan of Amplesound and have six of their guitars but I haven't tried their basses. Mostly in an attempt to protect my wallet from further damages.

Thanks for all the great responces so far, good information. 
Yes, I avoid 32 bit plugs.. I still love my "Mr Tramp" best of all whurly's but I now use others. 
 
I didn't notice that SI bass is not velocity sensitive.. It might be actually why it works so well for backing tracks. It will come through with the same tone no matter what the original velocity was. I rarely have to mess with even the level because I have that set in my pre set patch. I leave the channel at unity. 
I grabbed the Gibso Basses when They we're offered free I think, I remember trying them and not likeing at all, but I should try them again while I'm doing this. 
Anyhow, keep em comming

This is a free light version of a P
http://www.amplesound.net/en/pro-pd.asp?id=19

+1 to Cake's basses for RPro, especially Upright full. Craig Anderton's bass collection is great, sits perfectly in the mix. ST3 basses are really nice too. For key-switching and playability nothing beats Ample Sound basses.

A cool-sounding bass that people tend to forget is the non-upright acoustic bass.
 
Autodafe has a free sampled Ibanez acoustic bass lib (though it requires the full Kontakt 5):
 
https://www.autodafe.net/free-stuff/acoustic-bass.html
 
Also, Amplesound's one (of a Guild B54) is nice, though of course, not free.
 
http://www.amplesound.net/en/pro-pd.asp?id=17
 
There are tons of free bass soundfonts out on the web.  I found this site that has a few quality basses.
 
http://www.flamestudios.org/free/Soundfonts
 

Soundwise
Craig Anderton's bass collection is great, sits perfectly in the mix.

Thanks, sitting in the mix was the intention...i wasn't going for "fret-noise-and-all" emulations, but something with the same kind of playing feel as a synth bass but the sound of an electric bass. The Les Paul really cuts through a mix, the Midtown is great for pop and modern country, while the EB5 has eight different sounds so some will be totally inappropriate while others will fit a song perfectly. (If anyone wants to hear how they sound in a mix, all the electric basses in my "Neo"- album used the Gibson bass expansion pack.)
 
Although I don't really use it much any more because it's not as compatible with the kind of music I'm donig these days, the Scarbee Rickenbacker bass for Kontakt is outstanding.

Trilian is $300 but considering all you get it's actually a bargain. I've been using its non-standup acoustic bass and loving it.
 
1/3 of Trilian, however, is synth basses. And it lacks a Rickenbacker. If you don't care about synths, consider Orange Tree Samples' bass bundle. For $259 you get 4 basses, including the best Rick around as well as a superb acoustic.
 
 
 

Anderton

Soundwise
Craig Anderton's bass collection is great, sits perfectly in the mix.

Thanks, sitting in the mix was the intention...i wasn't going for "fret-noise-and-all" emulations, but something with the same kind of playing feel as a synth bass but the sound of an electric bass. The Les Paul really cuts through a mix, the Midtown is great for pop and modern country, while the EB5 has eight different sounds so some will be totally inappropriate while others will fit a song perfectly. (If anyone wants to hear how they sound in a mix, all the electric basses in my "Neo"- album used the Gibson bass expansion pack.)
 
Although I don't really use it much any more because it's not as compatible with the kind of music I'm donig these days, the Scarbee Rickenbacker bass for Kontakt is outstanding.

Might I ask where you basses are availble to buy Craig A. ?