Do not get clown-loaches. They get huge and won't fit on your tank once they grow.
My favorite fresh water fish that looks like saltwater fish is the dwarf puffer fish. So darn CUTE!
They kinda look like a ballon with eyes and kissing lips. The problem is that they wouldn't go with the fish you already have, as the puffer fish are agressive and best kept within themselves...
As the ferret said tiger barbs are also a good candidate (they don't look anything like nemo but are nice fish), they are wonderful fish that aren't shy at all, but note on the tiger barbs you should get a group of 6 to 8 because otherwise they will chase your other fish to exhaustion...