What should I buy? Game or Games, there's a challenge for you guys and gals
Keep an eye out for weekly specials. I don't know what you can get for less than 400 points. If Microsoft is still letting people get MS rewards for using Bing, you can score 400 free points every month or so. Sorry I can't think of anything else.
You can get the new alien DLC for A World of Keflings that comes out tomorrow! :D
Remember: Death is only the beginning.
There are some excellent indie games out there. OXM gives reviews on the best ones and there reviews are pretty spot on.