Arcade

Dario Accornaro's TheZone is an excellent one-player asteroid game with a huge playing area and a spaceship which is always centered. Collect goodies and shoot at easily annoyed aliens.
Michael Hanson's Asterax (459K) allows for two simultaneous players which move about the screen. Emphasis lies in collecting money to upgrade. I recommend using the ship with the best shields and purchasing insurance wisely.
John Stiles'Skittles looks a lot like Doctor Mario except that there are more colors and the dots only have to make contact, not necessarily in rows. Play versus the computer or in exciting two-player competition.
Tetris Max is generally agreed to be the best implementation of tetris for Mac. There are many options, including two types of drop keys and customization of music and graphics. Also try Texris for two players.
ThreeTris, similar to BlockOut, transforms tetris to the unique in 3D. Unfortunately (perhaps) this version has few complex pieces.
Michael Weyandt's Meat Gone Bad is a vibrant variation of the Space Invaders theme with good sound and graphics.
Tuan Huynh's Space Junkie is vaguely similar to Galaxian. The aliens, as they drop bombs on your ship, move in different patterns each level. Try to keep from overheating your gun.
Ingemar Ragnemalm's Bert is a spin-off of Q-Bert with enough levels to make you corrupt.
Check out various PacMan Clones.


Slick Control

Jason Rainbows' Garcia's Guitars uses free planar mouse movement, which is very smooth and may take some getting used to.
Richard Bannister's Space Debris is a clone of Crystal Quest. Instead of numerous, the aliens are progressively more aggressive, which though difficult contrasts with the original in higher levels.
Michael Fan's Munchies uses the same type of mouse control but is more fun to play. The collected objects, food items, dash around trying to avoid you.
Kevin Quigly's Space Cab can be played with a mouse, though I prefer to use the keyboard to fire the taxi's thrusters as customers are shuttled through different levels.


Fighting

Phil Stroffolino's Renegade Space Ninja has its own set of characters and special moves. The drawings are large and the movements smooth with adjustable speed settings. Though fairly easy to beat, it also has two-player combat.
Adam Winiecki's Grizzly pits stuffed animals against each other in paw-to-paw combat. One or two players.
John Dalgliesh's Clash of the Dark does not have speed limits and plays extremely fast on my machine. Two players only.