The US Xbox 360 site has some new XBox Live Arcades games listed which should mean it wont be long till they are available.

Crystal Quest - The 1987 classic is back. This updated and enhanced version allows you to pilot your ship through 60 waves, collect crystals, and evade baddies. Grab all the crystals to open the gateway at the bottom of the screen, and don't forget to gather up the goodies in each wave!

Marble Blast Ultra - Travel back to the 'astrolab' arena in Marble Blast Ultra to navigate your marbles through moving platforms and dangerous hazards, or go head-to-head in ultra blast multiplayer mode, racing to collect gems to see who ultimately wins all the marbles.

Feeding Frenzy - Slurp, gulp, and crunch your way all along the Frenzy Coast in Feeding Frenzy! The rules here are simple: Eat anything that's smaller than you and swim clear of everything else. The more you eat, the bigger you get, and the bigger you get, the closer you come to taking on the fearsome Shark King.

Astro Pop - Blast off with earth-shattering arcade puzzle action! Match four bricks, use combos and powerups to score big points! Two different gameplay modes, coupled with 33 challenging bonus rounds, offers hours of extraordinary replay value for players of all ages.

More info here.