Good freeware games?
Here's my collection:
I Wanna Be The Guy - Immensely challenging platformer. Only expert gamers need apply.
Eversion - Deceptively cute platformer hiding a very dark secret. (Author's warning: not intended for children or those of a nervous disposition.)
Cave Story - Quite possibly the best freeware game ever. Good characters, plotline, gameplay, sidequests, music. A 2D shooter/platformer hybrid, kinda like Metroid without quite as much exploration. You owe it to yourself to play this game.
Blue Wish Resurrection + - freeware shmup somewhat reminiscient of DoDonPachi. Challenging without being unfair, with some really nice music.
Eden's Edge - another shmup, same designer as BWR. Somewhat simpler but still highly enjoyable.
Fraxy - boss rush shmup in which you can download bosses made by other people. Quality depends on how good the boss maker was.
I have quite a few more shmups, but those are the best.