is a fantastic rogue-like RPG that I'd recommend. Looks great, neat soundtrack and a lot of playability makes it last a very long time.
is also a really neat game which was made in a short amount of time and has a Gameboy look and feel to it.
Of course, I also enjoy The Kingdom of Loathing
since it's my favourite single player browser based MMORPG with loads of re-playability, regular updates, additional content and fair donation goodies.