Keyboard only games

dwarf fortress

140 is pretty good, but also really short. (1-2 hours)
Thomas Was Alone is great too!
And depending on how you play it, Super Hexagon is also keyboard only. Great game, took me 15+ hours to 100% it.

Perhaps some racing games.

Castlevania?

I'm pretty sure you can play Jamestown and Nightsky without mouse.

Braid and EDGE are playable without mouse.

all jrpg - countless hours without mouse :D

One Finger Death Punch is great fun.

get "the cat lady" all you use is arrow keys on the keyboard and its a great game.

The first that came out of my mind was Chicken Invaders. Good oldie free game, great memories.
Every racing game;
Super hexagon;
Uplink;
Sonic...

All I can think right now.

Sega Genesis and Mega Drive collection if you like RPGs.

I'm actually doing Phantasy Star 2, 10 hours of gameplay and not even reached half of the game.

Wonder Boy in Monster World is also a great game that will take you much time.

Otherwise, you can try the Worms Armageddon, Fortix, Superfrog HD, TrackMania (United/Canyon/Stadium/Valley), Ultionus, Pac-Man Championship DX+, Offspring Fling, Jamestown, eXceed 3rd, etc.

Any racing game or indie game that looks like retro gaming should be playable only with a keyboard.
I just made a list from my library, I'm also playing on a crappy laptop I can only play crappy games. (for the moment)

Risk of Rain

if i were you i would invest 5$ in geting a gamepad

Risk of Rain is a good one, like inn0s suggested.

Electronic Super Joy or mostly every other platformer game

You could give LIMBO, CaveStory, and Stealth Bastard a try.

Typing of the Dead: Overkill

Guacamelee
FEZ

Buy one less game and get yourself a mouse.

Super Meat Boy :D

DMC3 and DMC4

Pid; Tomb Raider I, II, III, IV, 5;