If I were made of LEGO-style bricks, I would have an extra arm at the center of my back. Sure, it would make sitting down awkward, my shirts would never quite fit, and buying gloves would be kinda pointless, but... Please? Can I have it anyway?
Bombermaaan (Windows, 2.2MB, free) - A free, open source, in-progress clone of the 16-bit Bomberman game. The same brick bombing power-up collecting enemy 'sploding action you know and love, now in PC flavor! Creating new levels is as simple as typing in a text file, and the game supports up to five players on a single computer.
Scrollbit (Mac/Windows, 1-4MB, free) - A minimalist racing game that is so outlandishly entertaining, you'll catch yourself laughing out loud on more than one occasion. You must have a mouse with a scrollwheel to play (sorry, laptop users), using it to change direction up and down. Hold the [spacebar] to accelerate. The faster you go, the more scrollwheel scrolling you'll be doing, and the results are often fantastically amusing.
Bricksmith (Mac, 7.2MB, free) - For curious to serious Lego model builders who want to create new designs and even share those designs with others, Bricksmith provides the tools to do so. Complete with every Lego part imaginable, the Bricksmith toolset is a model builder's dream. Zoom in or rotate the 3D display, even create your models using "steps" to allow someone to see your model being built one brick at a time.
Calamity Annie (Windows, 5.3MB, free) - A quick-draw arcade game of reflexes created by auntie pixelantie, Calamity Annie is as old-school as it gets. Face off against two dozen foes in one-on-one duel-style battles. Keep your weapon (in this case the mouse cursor) in the holster area while the screen is black, and as soon as the lights turn on, move and shoot your enemy as fast as you can. You only have three lives to dispatch all of your opponents, so there's no room for error.