I have a lot of virtual instruments and sample libraries, but Native Instruments Scarbee Rickenbacker Bass is one of the best values ever. It is under $100 and is the most versatile and well-executed bass VIs or synths I have tried. It covers all the articulations, and the set of presets would be all most people would ever need, although you can tweak things to your hearts content (or run it through a separate amp simulator if you like).
For me, this is right up there with Ivory II and RealGuitar—something I don't say lightly.
Of course, if you don't like the way Ricks sound, you won't like this, but I think a Rick is perfect anytime you want a bass line to stand out without blowing the subs. With Ps and Js I usually have to crank the 1-1.2K band up +5db or more to get the bass distinct. With the Rick, using a bridge pick-up preset (like Bridge Pure DI), or the one of the doubles (like Double Date or Both Pure DI), it just jumps right out without too much boom. Of course, there are some heavy low-end settings if that's what you need.
This would encourage me to pick up Scarbee's P Bass and J Bass as well, although I am in less of a rush since I can cover those sounds with other synths (though probably not as well as if I had the Scarbee versions).
By the way, I almost always have installation or authorization glitches with new stuff, but this downloaded and set-up without a problem.
Peace, The Mighty Konrad