My goal for this site is more so to help commercial software developers get reviews and attention for their games... especially when such attention is justified, but there's so much free stuff for the Android that it just can't be ignored.
For a start, there's Asteroids by Mark Mainwood. A remake of the classic Atari arcade game of the same name featuring the original vector graphics. The game plays pretty well with the DPad and keyboard on my Droid, but without it I doubt this game would be too enjoyable. I just don't see trackball control working too well.
Next, we've got Colossal Cave Adventure, from EC Software Consulting, which is a remake of the old "Original Adventure" from the 70s. Pure text. Simple interpreter. Obviously you'll need to be comfortable with your keyboard, whether on screen or off screen, to play this with any satisfaction.
Deflektor, from Jompe71, is a remake of the old C64/Amiga game where you're trying to use mirrors to bounce the laser beam from entry to exit. The screen doesn't stretch to fill up my Android's full screen, but otherwise (sound, graphics) it looks pretty well done ad has all 60 levels from the original.
Frozen Bubble is a game from Pawel Aleksander Fedorynski and I'm a bit surprised this isn't being charged for given the quality. It's a Bust-A-Move style game where you're shooting bubbles. When three like colors are attached they explode and anything not attached to the top of the screen falls away as well. You're goal is to clear the screen of all the bubble. The touch screen controls are great and I see it's developed by a Google employee in Europe.
Lumbricidae from Amoneron is an odd title where you're using the accelerometer on your Android device to control a worm and lead it through tunnels. Eating soil causes you to move more slowly. Drinking oil causes you to speed up. Oh, and you're being chased by the rising water table. It really wasn't my cup of tea, but it was free.
Meteor for Motorola DROID is a game that I can't tell whether it's free or a demo. It's from Mobile Stream, but has a similar icon to Chillingo's Meteor game. Add to that the fact that my icon says it's a Lite version, yet I don't see a pay version and I remain confused. In any event, as it stands now it's an excellent and free Breakout or, more accurately, Arkanoid clone.
SFCave has been reviewed before and is still a favorite that I play almost daily.
Twisty, from Twisty Team, is a Z-machine interpreter which means it plays the old Infocom games as well as a myriad of newer games based around that system. It includes 3 sample games including the aforementioned Colossal Cave. Colossal Cave seems to work fine, but the screen is messed up when I try the other two. I haven't tried any of the Infocom classics with this software yet, but am sure I will eventually.