other fish

There's not really any fish that will interact in a "pair" kind of relationship with your percs., however, if you mean what kind of fish you can keep with them, the possibilities are quite vast. To make any educated suggestions, we first need more info:

Tank size, filtration, live rock, etc.

Are you planning on keeping corals or invertebrates?

What kind of fish do you prefer? Smaller fish? larger fish? Colourful fish? Personable fish?