The first game I ever made, Unga Bunga is a multiplayer platform/deathmatch hybrid for 2 to 3 players, in which the players run around as club-wielding cavemen in exotic habitats, kill moose and bears to gain technology (which allows them to use better weapons, including spears, traps, firesticks, coals, bow and arrow, sword), fend off invading philistines, and ultimately compete with each other for various objectives (depending on the game type). An amateur effort, but still a lot of fun. Note: this is a multiplayer-on-one-keyboard game only; no single player mode exists.
One of my all-time favorite indie creations, N is a brilliant, minimalistic take on Lode Runner, and other classic platformers. Superb controls, a great physics engine, wonderful level design, and pure ninja goodness combine to make this one a true classic.
Be forewarned: this game takes time and dedication to appreciate. However, if you take that time, you will find in Dwarf Fortress one of the most amazing and complex simulation games that you will ever play. Combining aspects of roguelike, strategy, and "god" games, Dwarf Fortress has two modes of play: Fortress, where you oversee a dwarven civilization, and Adventure Mode, which plays like a typical roguelike game. To date I find Dwarf Fortress to be one of the most amazing games ever made, including all commercial offerings, but like I said: be warned that the game is not easily accessible! For help, look to the wiki. Also, try out Mike Mayday's Graphics Edition of the game.
Among the best independent games released in the last ten years, Cave Story is a traditional action adventure in the vein of old classics such as Metroid and Castlevania. It was five years in the making, and every detail shows off the love and care that went into its production. If you only play one indie game this year, make it this one.