Static, I love how you don't like Small Arms, yet included it...

I still think I might buy that game someday.
OK, I am ready for an in depth look at my picks...
Original
1. Band of Bugs - Just plain fun. Leaderboard chasing is a lot of fun, and the multiplayer just keeps you wanting more. You can chose between three completely different styles of multiplayer too! Regular NinjaBee stuff, and they put some sort of awesomeness potion in their games.
1. Cloning Clyde - Again, leaderboard chasing was really cool, and co-op was done really well on this! Classic original NinjaBee work!
3. Marble Blast Ultra - Great fun puzzle stuff, while still being action packed. Multiplayer was alright, but not as good as the above two titles. Where was the DLC for this one? Felt great getting my final par time for level 60...
4. Outpost Kaloki X - My first 360 arcade experience for an original title that wasn't anywhere else (on consoles), and was completely awesome. Great long story, awesome humor, and DLC. I was delighted when I saw the developer kept all of that for their games! (Save DLC for CC...

) I never was a huge fan of tycoon games, but this was just neat for a weird reason.
5. Eets - I love these types of puzzle games. Change the surroundings so your character can win. The Mario vs. Donkey Kong games did this in a cool way, and this had the same feeling. It is extremely long, so long I still haven't finished it.
5. RoboBlitz - The physics are what made me want it so bad. It controlled in a really cool robotic way that was fluid yet still mechanical. For some reason that was a selling point. The story wasn't great, but the missions were. I don't just spend money on any Arcade game, so one that can make me spend 1200 points is doing something right.
Honorable Mention - Hexic HD - The only game I had when I got my 360. I got PDZ the next day, but this was still surprisingly addictive. Unfortunately it was more fun playing multiplayer on MSN Messenger with my friend (who also has a 360). Maybe Hexic 2 will be worth it, but I highly doubt it. I never could master it though.
Old Stuff
1. Sega Games! - It is a big tie because the games themselves aren't really that awesome after I beat them... it is just the fact that I hadn't played these games in years! One thing you can put under all of these is that they took of hours of my life when I was younger.
* Sonic the Hedgehog - Save anywhere you wanted to! I never dreamed of beating this game with no deaths, until I just restarted to my saves.
* Golden Axe - Online and offline co-op! I didn't think they made games like that anymore!
* Ultimate Mortal Kombat 3 - Offline multiplayer, and just recently I got to having fun in online games. Too bad it lags a lot online for me. Why couldn't it be like BoB, which is entirely lagless!
2. UNO - For only $5, the price of an UNO deck, I have spent 26 days on my Xbox playing UNO (according to 360voice). Online is fun with friends, even when nobody is paying attention to the game whatsoever.
That was a total of 4 games, but the only other established games I have (Robotron and Texas Hold 'Em) are not worthy to be on the list. Sorry.