I agree, clown loaches love caves and places to hide. (See my post on here, What a Day.) However they do get very big and do not do too good on their own, you should really have at bear minimum 2 of these but idealy you should have 3 or more.
Clown plecs don't really get very big and should be ok in a small tank, they will do a good job of keeping algae levels low too seeing as though they are algae eaters. Corys are also pretty good fish to keep in a small tank and there are loads of different breeds of them, they will keep the bottom of the tank pretty clean too as they eat a lot of the food that sinks to the bottom that the other fish miss. Corys also like caves and places to hide.