The Uncharted series and the Ratchet & Clank Future series are phenomenal. Since they both had sequels released recently, you should be able to find the originals discounted.
One thing to keep in mind about the R&CF series is Quest for Booty which is a download only, but stand alone, second entry in the Future trilogy.
tecnowraith, judging by your comment on FPS', I'll assume you have a gaming quality PC. That being the case, get your RPG fix there with games by Bioware (Dragon Age, Mass Effect 1&2) and Bethesda (Fallout 3, Elder Scrolls), to name a couple of the big companies.
You didn't mention whether you have a 360 or not so I'll mention multi platform games just in case, anyway here are the games I've played and really liked.
LittleBigPlanet, basically an old school platformer, with level creation tools and a stupid number of user created stages to go with them. More pure fun than any other game I've played since it came out.
inFamous, it's an open world game similar to GTA, but instead of a criminal protagonist you play as someone with electricity based superpowers. One of the best games of the year.
Batman Arkham Asylum, has already been discussed so I'll just say this, it perfectly captures the essence of Batman in a great game.
Heavenly Sword is a good action game similar to God of War. It is really, really short (sub ten hours, and not very close at that), which makes it hard to recommend buying for more than twenty dollars.
Assassin's Creed 1&2, I liked and enjoyed the first game, but I acknowledge the criticisms of it (the mission structure is repetitive). The second game is just about an across the board improvement upon it making it an all around excellent action adventure game.
Prince of Persia is a good fantasy adventure game.
Tomb Raider Underworld is another good adventure game.
If you ever played and enjoyed a Metal Gear Solid Game MGS4 is must play. One of the two reasons I chose the PS3 over the 360.
And Finally you have Uncharted 1&2, third person shooter action adventure games. Gears of War is frequently reference for the gunplay (haven't played that myself, so I can't say), throw in some Tomb Raider style exploration and helping of Indiana Jones and you have an idea of to expect from the well polished games.
Oh, the other reason I picked the PS3 is coming out a month from now: God of War 3.
Personally, I would note that games like Batman and Assassin's Creed 2 share a lot of similarities in gameplay (puzzle-solving using special senses, combat based on timed responses, stealth attacks, lots of climbing around and of course lots of wonderful toys). They offer an amazing gameplay experience, but that experience only lasts maybe twenty hours, even with hunting for feathers and Riddler trophies and what-not. If renting's an option, I'd go for that.
Batman yes, AC2 no. I spent over thirty-seven hours on AC2 and didn't even try to get all of the feathers, I did collect everything else however. I'm sure I'd still be well over twenty hours without all of the collecting.