Lets see.
Amnesia - is kind of fun, yet scary First person type deal.
M.U.G.E.N - Free - 2D fighting game, its fun because if you can think of a person, you can probably put them in the game. If you learn to input characters and levels in correctly [and find the ones that don't suck.]
Night Sky - 2D puzzle type game. You might find more amusement than I did with it.
Super Mario War -Free- Small 2D game where you try to stomp the other players. Also comes with a variety of game modes. I found it satisfying along with the ability to make levels. You can also find other characters and levels online as well.
Kyntt - Free - Short fun 2-D platformer with interesting areas to discover.
Within a Deep Forest -Free- Puzzle game where you are a ball. The story is kind of shady.
Cave Story - Free - 2D shooter. Best free game you'll ever find.
Touhou -Unsure- Impossible bullet hell games and some 1 on 1 fighting games.
Windom XP -Free- 3D game where you pilot a robot and take out other robots. -Gundom Ripoff-
Lemming Ball Z alpha -Free- Pretty much Dragon Ball Z but 2D and kind of humorous. [Fun for about 4 hours]
The ones that aren't free can be pirated -At your own expense-
--Edit--
I'm not even in Piratez lelloleoleolee