For fast block speed there is GeistGeld (XGG), merged mined with Bitcoin it is the fast small-change transactions chain of the merged mined family.
It likes to use 4 or even 5 or more gigs of RAM though, do all the very fast block chains do that, at least once they have been running for a year or two? Still RAM is getting cheaper all the time as as you said speed is a pretty nice feature.
-MarkM-
I'm not really sure, Liquidcoin doesn't really have a block speed. Just as fast as people can mine 0.05 diff blocks.
It's pretty much permanently stuck in early adopter mode.
And the rate of reward decay was very quick.
Excellent premining opportunity.
I think I got 50 bucks out of it with a core2quad.