Overall, for space-age games, I think it'd have to go to WEG's d6 Star Wars.
Other ones I've enjoyed:
Alternity: great system, though XP costs need to be simplified somehow.
Fading Suns: Imagine Dune, before the birth of Paul Atredes.
Star Trek: I really liked the Last Unicorn (best)/Decipher version. FASA's version didn't feel right and for as much research they did, they got a lot of information incorrect.
Space 1889: A wonderful setting, rules were so-so and the adventures were horrible, horrible railroads. Red Sands - which is Space 1889 for Savage Worlds seems a lot better.