40B is a nice size, especially starting with a blank slate like that. What appeals to you?
I personally love those dwarf neon praecox rainbows. But there are a lot of really good options. If it were me, I'd look into one fish that I really wanted, and then go from there compatibility-wise.
Also, if you like catfish, check out hoplo catfish (see my avatar). They are basically hotdog size cories, non-aggressive towards any fish and social with each other. For some reason they aren't that common, but they are super easy / hardy and have good personalities. Just can't have them with particularly aggressive fin nippers - I had one named "Stumpy" for this reason...