Mirror's Edge is fun. You could probably find it for cheap. It's a 1st person game that focuses on parkour, instead of dumping lead. The Xbox Live Arcade is full of plenty of amazing games, and all of them can be demo'ed I think. Shadow Complex, Limbo, The Dishwasher: Dead Samurai... All amazing games. I stopped buying retail games for a while, simply becasue the Arcade is fantastic.

Borderlands 1 & 2
Fallout
Lost Odyssey(Final fantasy style RPG)
Metal Gear solid HD collection
Assassins creed
Trials HD & Trials Evolution (XBL Arcade)

XBL Arcade games worth trying the free trial download:

Shadow Complex
Ms. Splosion Man
Mark of the Ninja
Outland

Borderlands I agree with.

there's a game on XBL called N+. It's a basic platformer/puzzle game. You're a ninja, find your way out of this crazy room, pretty much. I was sooooo addicted to that game for a while. Definitely worth checking out

You should check out Skyrim, a lot of gameplay hours and DLC that will extend the life even more.( I would also recommend Morrowind as it is backwards compatible on the 360, but it isn't easy to find at stores.)
Red Dead Redemption
Dead Space 1 and 2
Dragon Age: Origins
Fable series MAYBE.. it's alright...Not three so much. >>
Oh and Unreal Tournament 3 is an older FPS 360 game but has solid multiplayer. : P

Outside the big names like HALO, BF and COD.... what are some suggestions. I originally got my Xbox for sports games but recently got addicted to HALO so much so I went out and bought them all (Minus 2 as I can't seem to find that one at the local shops - yes I know it was made for Xbox and not 360 but it is backwards compatible from what I've heard). I picked up Lost Planet at Game Stop for $2 and after about an hour got rather bored with it. Big fan of the Mass Effect series as well so

Suggestions? Anything at this point.

Sell it and get a ps3. so many more (And better) games there. I have both consoles. pretty much halo and mass effect were the reasons to have an xbox but now bungie is writing for all platforms and microsoft has halo.. mass effect is on ps3 and you have uncharted tomb raider last of us ratchet and clank assassins creed borderlands ect ect on ps3 there is a lot more variety.

xboxone sounds like it's going to be terrible and not a lot of content. I"m ditching xbox myself and I'll be picking up ps4

If you're looking for something different I second the braid suggestion. It is a 2d platformer with a pretty unique time-based gameplay mechanic. Limbo is pretty cool too if you want something a little dark and artsy. Another 2d platformer. A bunch of the big name titles were already mentioned so I figured I'd throw out some more indie ideas. If you want to have a life and play something really old school, check out I MAED A GAM3 W1TH Z0MBIES 1N IT!!!1. It's nothing life changing but it's pretty chaotic and the song is awesome. Super Meatboy, Shadow Complex, and Fez are all supposed to be good as well.

Splinter Cell Series (conviction specially its awesome)