I second The Orange Box. That has to be one of the best value packages ever released and will give you lots of different kinds of games. You're bound to find something you really like in there.
You might also look into Chronicles of Riddick: Escape from Butcher Bay. It's a bit old (came out in 2004) but the graphics were great at the time, still looks pretty darn good. It's mostly a shooter, but it has a very small RPG element as well. It also has some great action sequences. It is even easier to recommend because of the fact that you can purchase a used copy for well under ten dollars.
Not sure about this as much, but have you played Oblivion? It's not everyone's cup of tea, but there is a tremendous amount of game for the money, and it's very well polished. You might look into that (play the demo or a friend's copy before buying).
If you have even a passing interest in World War II shooters, you should also look into the Brothers in Arms series. Again, used copies should be found for very cheap, and the authenticity and grittiness really makes these games enjoyable.
One last recommendation; the Jedi Knight Series. They are actually decent, albeit unrealistic shooters. Add that to the crazy fun you can have with the force and lightsabers, and you have yourself a game! This is another title that can probably be found used for less than five bucks, so give it a shot if you are at all interested in star wars.
That's all for now, good luck in your search!