If you had a big tank............

Gotta go with Discus and a good sized school of Congo tetras. Those fish are not that large I guess but would look good.
 
I would have a large school of Zebra Loaches and Peppered Cories at the bottom, a very large school of Cardinals and Rummynose Tetras, and a few dozen Guppies.
 
I have a 300, and my 'monsters' (none of them are very big yet) include golden shiners, red-spotted sunfish, and warmouth; hopefully soon I will add some central stonerollers, northern hogsuckers, stonecats, and longear sunfish. None of these are comparable to pacus or aros, but they're big enough to fill a 300 pretty thoroughly.

If I had a BIG big tank (1000 gallons plus), I would keep some of the 'primitive' fish like bichirs, bowfin, and gar. Those guys have always fascinated me.
 
AquariaCentral.com