I have whitecheeked gobies (FW) and they are characters. strictly a lower level fish though- maybe for the upper levels a little school of threadfin rainbows? dwarf cichlids would be cool too.
How about dwarf puffers? A tank at around 20-29 gallons should be able to house a couple of them at least. I've done some research on them, and they seem to have quite colorful personalities.
Richer - that is a great idea. I would just add that they are pretty messy little guys, so filtration (and water changes) are key. They are fun fish, and dont demand a lot of space. Good call.
Dwarf puffers are FW and like heavy planting, they are actually easy-care fish and the first easily bred puffer. As they do not top an inch, you need not go more than 3 gallons per fish - I currently have 5 in a 15 us gallon (~24x12x12).
South American puffers are FW, but have a strong requirement for basically an all-snail diet, so need support space for snail-rearing. One in a 15 gallon tank.
I also like the invert tank bit, currently have several. Ghost shrimp, Amano shrimp, cherry red shrimp, Bumblebee shrimp, Macrobrachium shrimp (some of these need a larger tank - there are giants in the group to over a foot); any of several different FW crayfish.
