Since funds are an issue:
The Orange Box, as a few people have mentioned, is great. For $20 you get five games, and only one of which requires you to play on Live mode. You can enjoy Half-Life 2, the first two episodic sequels, and Portal all by your lonesome without connecting to the net. So breaking it down, it's like $5 a game. And if you do go on Live, you get Team Fortress 2 which is always good for a laugh.
If you're into RPGs...I wasn't the biggest fan of Oblivion, but it's not a horrible game and it's selling for around $30 now. My biggest issues with it were the voice acting, the story line, and the setting. But I also thought Morrowind was the shit, so I may just be upset they decided to change everything I loved about the old game while making the new one.
Assassin's Creed has come down in price. I saw it for $30 recently. In my opinion, this is one of the best games out there right now. I love it, even with the repetitive missions and one-button combat. Yes it's M, but strictly for violence. And after a hard day at work, there's nothing that can't be cured by some hilarious background voice acting ("What is he doing? There's no logical reason for him to be doing that."), a sprawling open world, roof jumping, and, oh yeah, jumping off a tall building and stabbing someone in the face.
And if you're really broke, you can pick up the Prince of Persia: Sands of Time trilogy (made for the original X Box but still worth a play through) for about $5 a game at Gamespot. I love these games. They combine puzzles with platforming and great parkour style combat. In the vein of Assassin's Creed, they have some awesome acrobatics and I still enjoy the games even in comparison with current 360 titles.
