Check out this port of the arcade classic Asteroids by Doug McInnes. If you've never played Asteroids, or an Asteroids-like game, the goal is to pilot your deltoid spacecraft around the void of space, blasting large lumbering asteroids into smaller, faster, projectile-like asteroids, then blasting those into dust before they breach your hull and destroy you. Destroy or be destroyed is the only law against the impersonal Astroids.
Moon Rocks is an impressive little shooter-defense game that's pretty challenging and fun. Loosely inspired by the classic arcade game Missile Command, you defend your little chunk of the planet's surface from an onslaught of asteroids, ice comets, enemy ships and plenty of other things that threaten to turn your base into Swiss cheese.
Jussi and Marko, Flash game developers at OOPixel, borrow a little gameplay from several classics and wrap them all together into one nicely polished and addictive game. Asteroid Adventure is an arcade action game that will be both familiar and new to anyone that has played Asteroids before.
Chris Benjaminsen of Cosgames has come up with a simple and yet intensely effective multiplayer version of the classic arcade game, Asteroids, playable in any browser with the Flash plug-in. Each player (up to 16 in a room) pilots a ship in an all-out deathmatch, melee style, with the objective being to rack up more kills than deaths. Mad multiplayer mayhem, classic arcade style.