this link will take you to a page where you can search for all the packages available through the aptitude package manager.  The command to download these is: "sudo apt-get install [package], then to run them, you just enter their name in the console

a few to try out:

elinks - a browser that will run directly in your terminal. while not particularly useful if you already have a gui installed, its still interesting seeing what all of your favorite sites look like in a purely text-based format.

pacman - pretty self explanatory

nethack-console/nethack-common - a text based dungeon-crawler game. the -console version will run in the terminal, while the -common version opens a stand-alone window with the game running in it. May take a bit of effort to learn, but can be a fun time-waster once you do.

and while not an aptitude package, try running: "telnet towel.blinkenlights.nl" for a bit of fun. (you can do this in window too, but you will need to enable telnet.