The deadline for the Nickelodeon Writers Fellowship is Tuesday, February 28. You can apply with a live action or animation half-hour comedy spec (click here for the rest of the submission guidelines). It does NOT have to be a kids' show.
If you get to the next round of the competition, you'll need to have a SECOND comedy spec (so get writing!). For more information, read my interview with Karen Kirkland, Executive Director of the program.