There are lots and lots of freshwater gobies!
Numerous Stiphodon species are sold, including some superb "freshwater neon gobies" with brilliant blue or golden colours. These are mostly mountain stream fish that need cool, well-oxygenated conditions like those used for hillstream loaches. They aren't fussy about water chemistry, so provided you can get the tank right, they're not especially difficult to keep.
Then there's the beautiful peacock gudgeon, a spectacular soft water species from New Guinea. Their colours are simply amazing, and they're also easy to spawn, though the fry are very small and tricky to rear.
The Australian desert goby is just about the toughest fish in the hobby, with an ability to tolerate extremes of temperature, oxygenation and salinity. It's very easy to keep, and breeds without any difficult, the fry being simple to rear. It's a short-lived species, so you do need to get a colony of them going, but their colours are pleasant and they're very lively.
If you want something bigger, there's the Mogurnda species we call purple spotted gudgeons. These are medium-sized fish, typically around 12-15 cm long when mature, and tend to be boisterous, even territorial. But they mix well with peaceful cichlids and catfish of similar size, and they have excellent colours as well as very outgoing personalities. Unlike a lot of other gobies they're very omnivorous and will take pellets alongside the usual mix of fresh, frozen and even some green foods.
Cheers, Neale