Randall Munroe creates XKCD (there's a link in the sidebar).
He often inspires my cartooning side... When I get inspired I make some cartoons over at The New Yorker Cartoon Kit page.
Zachary Kanin’s “Heaven Help Us” Cartoon Kit entries accepted until May 16th 2010.
The backdrop and many irreverent characters and props are provided; you just drag and drop the icons you want, re size them, place them, write a caption and save to create your own LOL Cartoon.
Five winners are selected each month and are presented in a slide show for the gratification of your uproarious ego (and to make people laugh).
The New Yorker Cartoon Kit home page.