There's a time for every student, you're taking a class that you'll never think about again, you're lucky enough to have a laptop in class, so you do what every self-respecting student does, check their facebook and emails. That's fine for some, but what do you do after that? Here's a couple links in order of recommendation (Oh yea, all of these links are to free sites):

P.S. Don't forget to mute!

Http://www.crazymonkeygames.com
CrazyMonkeyGames.com is a great repository of small-to large scale games of every genre. Some Personal recommendations are games like: Pandemic 2 or Strategy Defense 3.
Highly Recommend that you bookmark this site.

http://www.popcap.com
Popcap Games is full of simple easy to learn hard to master games that anyone can pick up and play in 30 seconds. Chuzzle, Bejeweled 2, Bookworm Adventures are some personal recommendations. I recommend that you bookmark this site.

Http://www.Miniclip.com
Lots of games. I don't have much experience with this site, but I would recommend Canyon Defense

Http://www.newgrounds.com
Vast Site, contains flash movies and games, mature themes, like sex, drugs, rock and roll, and crazed mayhem. Recommended to some, others may not like.

Http://shockwave.com
Also another large repository of games from every genre. The general style of animation on the site suggests a younger target audience, but there are still many games to appeal to all ages like super text twist, Redline Rumble, 3D Pool, and Risk.

http://magic.pen.fizzlebot.com/
Using any shape you can draw, move the red ball through the level so that it touches all the red flags. Sounds easy, right? Nope. This game will keep you thinking for hours. Very Highly recommended.

http://www.rawkins.com/games/do2/
Dolphin Olympics 2 is another great time waster. The point of this game is to rack up the highest score possible in 2 minutes by leaping as high as you can in the air and performing tricks. See if you can reach Pluto, or the restaurant at the end of the universe. Highly Recommended.

Those are just a few that come to mind, but I'm not someone who scours the internet. If you have any links to good free online games, you are encouraged to post here.

Eternal Slacker
-Aaron Siegel