Geometry Wars is actually only 400 points, or $5. Definitely one of the best deals on Live Arcade... But it's only 1-player.
Zuma is 800 points or $10, but there's so many levels and it's soooo fun. My fave Live Arcade game. Bejeweled is the same price, but I haven't purchased it yet.
I bought 2 cards with my friend's GameStop discount (came to $36 after tax). I picked up Geometry Wars, Zuma, the Penny Arcade theme, and both Penny Arcade picture sets. Still have more than 1200 points left... But that Mutant Storm game is looking mighty tempting.
And now this deal? Whoah ho, I may have to stock up on points, heh.