From Matt's thread.
As an alternative to Trillian, apparently Cakewalk has one included in it's pack for $49. No idea how it is, so Matt should buy it and let us know.
Cakewalk Studio Instruments Download - Mac & PC
Edit: Actually, for $49, I just grabbed it. Will post up a couple of test clips at some point.
[VIDEO]http://www.youtube.com/watch?v=mmQT534K3VE]YouTube - Studio Instruments - Bass[/VIDEO]