Must-own Xbox Live Arcade Titles

[Blix]

I'm getting a 360 in September (finally!) and I was wondering what are some of the truly amazing XLA games for the system. As I'm writing this I just saw that PS3 is getting Limbo so I think I'm writing that one off the list as I will get it as soon as I can. I plan on buying Hydro Thunder: Hurricane ( I loved the original on the DC) but what else is there?

I look forward to some recommendations.