I'm partial to
Diaspora (see sig), but I can honestly say that it wouldn't have happened without
SOTC --
Spirit of theCentury was the first game that everyone at the table wanted to run, and there was a great stretch of four weeks when we just passed around reffing.
From there, we wanted to take that engine and use it to recapture the feel of Classic
Traveller -- the Little Black Books we had played as kids. That's what
Diaspora is, really: SOTC hacked to boogie around space in a little ship.
There are a lot of good FATE games out there, and (now) many SF variants.
Diaspora is much more streamlined than
Dresden or
Starblazers: both in size (it's a single digest-size book) and in its conception (so instead of pages of stunts tuned for each skill, there's three pages about stunts to let you build your own).
If you want to see some of the rules the SRD (no examples) is available, but it's probably better to look at the
Spaceship battles chapter, which (if nothing else) lets you test out the space combat system and get a sense of the ruleset.
Hope this helps! Whatever you choose, I'm sure your friend will appreciate the gift.