Synth1. Its been out a long time as a Windows-only VST plugin and has been ported (in beta form) to Apple. By using a freeware AU to VST bridge, I can use it in either Garageband or Logic 9. The site is in Japanese, but there is English documentation available.
I put together the piece below using drum loops and 7 instances of the Synth1 for 9 tracks total. The CPU barely registered anything despite all the parts. The analog sounds out of this synth are very fat.
The interface isn't the prettiest but one great feature is that everything is on a single screen - no tabs, scrolling etc. so as a performance synth its pretty cool. It also supports MIDI learn to set up CC events or knobs to your hardwire.
The piece below features some bass patches - tweaked from presets and several tweaked versions of leads - one phased, one with heavy unison and one legato. There are thousands of free presets available for download on the web - just Google.
This plugin sounds as good or better than my (very expensive) Moog plugins from Arturia.
Here's what I put together with it - sort of just a jazz/funk jam session:
Honey Seeker by oldlibmike
Edit: Just more trivia of interest to synth heads maybe - The scratching section half way through the song was sort of serendipitous. I usually rehearse a part a few times before recording and I was working on the lead when I heard the cool scratching noise which was weird since I didn't have any such patch in the song. I realized that I had the wrong track selected - I was playing the bass line in a higher register instead of the lead line. I decided I liked the sound so I duplicated the bass line and played it in a new track - no scratching at all though just clean notes in a higher pitch. I wondered what was going on and finally figured out that it was the monophonic track along with its glide. when I played on the bass line with the other notes there, the "scratching" was the slide from the bass note to the higher note.
I finally got the sound by copying the baseline notes to a new track, recording the high notes for the "scratch" and then using a spectral filter to filter out the low notes since they tended to "click". So there - far more information than necessary.