My favorite "Virtual Analogue" synth at the moment is FabFilter Twin2. Its not the most complex synth in my collection, but the oscillators and filters are superb, and the interface is such a pleasure to use that I can program sounds from scratch in the heat of a writing session without losing any creative momentum:
Their simpler "One" synth is also very useful: once I have layered a few instances and added a few extra LFOs using my host automation it doesn't really sound so simple anymore!
I should declare in interest as I make video tutorials for FabFilter (including a couple covering Twin2: part 1 & part 2) but I actually bought both those synths before I made the videos. ;)
Another VA I've been hearing lots of good things about is ACE, but I've not tried it yet: http://www.acesynth.com/
If you want something more specifically bass oriented you could look at Trillian:
This does a lot more than just VA synthesis, but its more expensive. I don't have this one either, but Spectrasonics have a great reputation and I'm sure its very good.