For a 30 gallon I would recommend a few Ottos or maybe a bristlenose plec
When you said "cleans the tank" did you mean the glass? If so, my recommendations are above. If you don't intend the glass, but the substrate, try some shrimp, or a few cories...though they will only pick up food - not the fish waste...
My favorite catfish would be any of the corydoras also known as cory cats. They are friendly and playful little fish that go well in almost all community tanks.
They are schooling fish and need to be kept in groups of no less than 3, but the more there are the better for them.
Here's a link with lots of information, including pictures of them: