Looking for some light books to read, more details within.

I’m looking for suggestions for some light books to read, some science fiction preferably. Absolutely not interested in murder mysteries, romance, cooking/cleaning/gardening/diet. Other than that, I think most things are fair game. I’ve got a nice big well-stocked Barnes & Noble nearby, as well as a decent public library.
I don’t want books that require me to spend the whole day uninterrupted reading. Not do I want ones that I’d lose a whole day to.

My situation is that I’ll be taking the bus/train 8 times a week (4 days, but round-trip), ~30 minute rides each way, plus whatever time spent waiting for the bus or train to pick me up. And I need something other than tapping my feet to the beat on my mp3 player.
So I’m looking towards books. I’ve never been a big reader. My favorite book series, though, has been the Hitchhiker’s Guide to the Galaxy (which I am in the process of re-reading).

So if anyone could suggest any good books like that, or any greats from the Science Fiction genre, I’d love to hear see it!