All of those Websites offer one small comic strip each day. Some of them are a bit geeky, so you might not understand them if you don't know anything about Linux / D&D.
xkcd
![xkcd](../images/2011/09/xkcd.png)
hijinks ensue
![hijinks ensue](../images/2011/09/hijinksensue.png)
Penny Arcade
![Penny Arcade](../images/2011/09/penny-arcade.png)
The Perry Bible Fellowship Comics
![The Perry Bible Fellowship Comics](../images/2011/09/pbfcomics.png)
Realm of Atland
![Realm of Atland](../images/2011/09/realm-of-atland.png)