There is alot of options. what kind of fish are you wanting? for schooling fish then neons, rasboras, cories, ottos and many others are ok. if you are looking for other fish that dont school then i would go with other live bearers like mollies, platies and sword tails. i would have the mollies as last resort as they can cross breed with guppies and the offspring from the 2 usually has a very high death rate in the fry.