Few emperors have a more varied reverse program than Gallienus. He's got animals, deities, emperors, and a whole host of interesting reverses. He has a lovely selection of some of the major Olympians, and is often the most affordable way to get some of the more rarer ones, such as Apollo and Neptune. In order of hierarchy, here are my selections: Neptune Apollo Diana Mars Please round out this the pantheon if you can!
I also have a few of the more unusual deities. Asclepios Felicitas Indulgentia Abundantia I have unintentionally specialized in Gallienus; I have 35 examples which vastly dwarfs any other ruler. The low price and varied reverses are just too hard to pass up.