Seconded (thirded?). I've whiled away several hours over the past few days playing Vulture's Eye, a graphical Nethack fork. It takes a while to get used to the default keyboard config, but it works.
Also, Puzzle Pirates for some online play. Almost all of the essential puzzles can be comfortably played with the arrow keys or with light use of the trackpad, but again it takes a little bit of time to get used to playing like that.

I don't know if it was mentioned, but I enjoyed that game Cave Story.

I Wanna Be The Guy is also a keyboard-only game....

Knights of the Temple by StarBreeze (same people who did the Riddick games) is a competent hack and slash with a fairly enjoyable storyline. Not sure if a Netbook would handle the 3D though. Its one to play though if you like something light and fun.

Oh, and what about some nice RPGing with the "Eye of the Beholder" saga?

I KNOW that Braid won't, not unless the netbook is vastly different from mine

This game is ridiculously fun and hard. Great retro style gameplay.

Bomberman. :)

Try N.
If you don't know it yet, you'll thank me later.

Really? That's cool.

And thus noone will read my post about N - the game...