My old group mostly played RuneQuest -- way more than Traveller, actually. Since the last RQ campaign ended, though, I've gradually lost interest in the game/world (didn't like Hero Wars one bit), and if I were to start up a new game nowadays, I can't really imagine playing anything other than Traveller -- maybe Call of Cthulhu (I still like the BRP system).
Other games we used to play back in the day: AD&D1 (played this exclusively for years, but gave it up around the time AD&D2 came out and never looked back), Stormbringer (our introduction to BRP), WFRP (loved those adventures), Cyberpunk (we played this A LOT in the late 80s/early 90s), Amber Diceless (my most spectacular GMing failure), Dangerous f**king Journeys (I hated this system but my players all loved it -- the Necropolis adventure was really good, though -- a couple of us actually played in it at a con ca. '88 with Gygax as the DM). There were also many many other games we only played once or twice -- some we liked (Paranoia, Mekton, Boot Hill), many we didn't. I could never convince anyone else to even try Space:1889 or EPT.