Irridecsent sharks are good to have. Mine is about a foot and a half long, But I know they grow larger than that. They are very active and arrent very picky about there food, and they dont eat much anyway
Channels and Bullheads are good depending on what size range your looking for...
I have a featherfin syno that is ALWAYs out and active...
And I love my marble pim...
It really all depends on what size class your looking for