Gobiopterus, Mugilogobius, and Acentrogobius are three genera of brackish gobies. They're not very common though. Be forewarned, though, if you can acquire Gobiopterus, they are very picky and may not accept anything besides small live food.
Chlamydogobius eremius, the Australian desert goby, is an inland species which is incredibly tolerant of a wide range of salinities. Some people classify them as brackish, but I don't think it really matters too much. Their only habitat is small pools that are relatively unstable.