Kind of depends on your taste and budget. Golden Wonder killies would probably work. They grow to be around 4 inches, are bright yellow with red tipped fins, and will stay close to the water surface. They're very interesting fish, and at least in my area, are pretty easy to find and inexpensive.
If you like odd and/or cryptic, you might try an African butterfly fish or two. They will hug the water's surface. They've got giant mouths, but they are surface feeders and tend to leave other fish alone. Only issue with them is that if your tank isn't covered, they're prone to leaping to their death.