#5
How much are you looking to spend?
I am a fan of Rapture and have the LE version on my Sonar Producer sequencer.

http://pro-audio.musiciansfriend.com/product/Cakewalk-Rapture-Virtual-Synthesizer?sku=706746

For $200 you can get the full version. It will give you quite a bit of sounds and I enjoy most of the patches available.
#6
At the moment I want to see whats available and do some research into them etc. Then shop around and find the best the cheapest as possible really