I go through and search titles all the time, and I've found some really good cheap games, that I highly recommend.
Chtulhu Saves The World. - Done in a style similar to early Dragon Warrior carts on the Nes, this game gives you control of some awesome characters, including your main protagonist, Cthulhu himself, to redeem himself and the peoples of the land. The gameplay is really well handled here, and seems to capture both the actual fun of these games, as well as poking fun at the genre in general. It runs 800 live points, and is seriously worth it. I finished the game in just under 10 hours, and that was cutting corners. I really think any classic fans of the old turn based rpgs will have a great time with this.
Doritos Crash Course- I could not have expected the level of fun I got out of this. The game basicly puts your character/avatar on a ninja warrior style obstacle course, and gives you medals for completing it in a certain amount of time. So far, there are only three levels, but each one offers its own style of challenges. Good for everyone who likes a platformer, I'd say give this one a try. It can;t hurt, its free.
X-men Arcade/ Turtles in Time - Two classic beat em up's hosted on the live service, both retain the arcadey goodness of the originals. Turtles in time has been updated with new graphics, and looks amazing. The classic X-men still harkens back to hours of woebegone quarters, and dead sentinels as far as the eye can see. I loved both of these, and at 400 points a piece, they are still worth every digital penny.
South Park Let's Go Tower Defense Play- A tower defense game with an increasingly infuriating difficulty. I really liked how it worked elements of the show into the game, as well as making a really good, challenging tower defense game. It also has a metric crap pile of bonus content, including unlockable characters, master levels, and clips from the actual show. This is one of the more pricey titles and will set you back 1200 live points, but is well worth it.
Also, X-box live tends to pander to us classic gamers with a line up of older titles like Castlevania- symphony of the night, The first soul calibur, A few of the SNK fighters, the sonic games, and my personal favorite, the Worms Series. Every title here is something I own, and would love to play with any of the other forumites. Check it out, when you get the chance.