Same here. Just reading this makes me want to get another 20 tanks.
So as a start iv always loved angel fish and depending on where you get them they can be a good, hardy, long-living fish that can be fun to keep.
A community tank is also something that i haven't gotten around to and yes dragon is right. They can be fun but with guppies and platys you might want to make sure you have some experience with "crowd control." Trust me those fish breed fast.
A tetra tank is also something that would be a nice addition. They come in many different shapes, sizes, and colors. In one of my tanks i have black neon tetras, and neon tetras. I also have diamond tetras and they are very beautiful but in the store (like most tetras)they look ugly becuse of bad water conditions. Some one could easily pass by the tank of a diamond tetra with out a second glance because of their unusually expensive prices and dull coloration but once i took them home and gave them the right care their whole bodys lit up like a christmas tree. Like their name said they truly sparkle like diamonds.
One more breed of fish that has been my favorite are tiger barbs. I unfortinetly have not had a lot of experience with them since they all died in the prosses of cycling one of my tanks. But they can grow large and they not only come in orange and black but sometimes green also. They are know to be fin nippers and should not be kept with other fish that have long, flowy fins.