Here are a few:
Strike Legion by Legionnaire Games - sort of a spiritual successor to Dirtside, has a fair bit of crunch but the core game is straightforward. Comes in a compendium now, with options for things like organic "vehicles", supertech (nano tech and computer viruses) and steampunk if you want them. Has its own background, but flexible enough for just about anything. I'm using it for Traveller and Hammer's Slammers. Downside is that sometimes there are too many options and weeding them out (like the really anachronistic VSF stuff) is a pain.
Laserstorm by Nordic Weasel Games - fast playing game in the NWG style, I don't have it but I like NWG's style in their rules I do have.
And Dirtside is still pretty good, I don't think you'd go wrong with it. Several human types and a couple of alien races exist in the GZG universe, not sure if they're in DS per se. But the weapon and tech options will let you build different types of units.
Chris