With the X-Files coming out with new episodes, the interest in 90's-esque alien invasions is on the rise. After having worked on the rules for some time, Crossover Minis feels it's time to release their UFO Squad set of skirmish rules.
The game uses the Song of... set of rules (you can find those rules in quite a lot of places, actually) and has a built-in campaign system. Crossover Minis has several sets of figures for the game up on their website as well. However, they do say that you can use any alien or other sci-fi minis you'd like.