If you want some analog-esque warmth, give the arturia synths a go. I have the cs-80v, the 2600v, the moog modular-v, and the minimoog-v, and they all sound great.
The modular is the most flexible and cpu hungry,
the mini is the simplest, but has the classic minimoog sound,
the cs-80 is capable of some gorgeous pad sounds among other things,
and the 2600 can create some fantastic sound effects, and some really great funky sounds.
The most unique and interesting is probably the cs-80 if thats what you're after, but if you want more info, check out
http://www.arturia.com, or post here with more questions.
If you want someting more digital, go for some of the other suggestions, or if you feel brave, try Reaktor.
XPM