In addition to some rebranded Bachmann figures, their product line used to include N Scale "scenes" or mini-dioramas (which Noch also did—to excess, and not as well as Busch) that combine a few bits of scenery, possibly a vehicle, and a few figures of unknown origin. Everything has since been discontinued.
Incidentally, if you happen to be looking for some N Scale extraterrestrials, their kit #1010 (released in 2000) is for you. It includes a UFO with various lighting effects, four aliens and one robot.
Where to Buy
Busch products are relatively easy to find worldwide, although their figures and scenes only appear on eBay from time to time.