Traveller. Average Joes wandering the stars, you know, like Firefly: fly your ship from planet to planet, meet people, get into adventures. Probably my very favorite RPG. The current edition is just fine for all your "science fiction adventure in the far future" needs.

Paranoia. Great for one shots. Not so much for lengthy campaigns. The 2nd edition was probably the funniest RPG ever written - it's entertaining just to read. The XP edition is pretty good too, and is what I've used most. I'm not very familiar with the current edition simply because I couldn't imagine how they could improve on perfection.

The One Ring. A great way to adventure in the actual Middle-Earth, with quite good mechanics. By setting the game between The Hobbit and The Lord of the Rings it does a good job of avoiding what I call "second fiddle syndrome" - playing nobodies while the book's original characters go and do all of the important stuff. And none of the players are spellcasters, so it's a nice change of pace from D&D. Either edition is good.

Legend of the Five Rings - colorful psuedo-Japanese fantasy gaming. Samurai and Ninja and weird freaky monsters from Asian mythology. Exploring and interacting with the setting and how it is different from your typical D&D setting is the whole point here. The 4th edition is my favorite version, though I really liked the original back in the day.