Project Blog.
The blogathon is taking a rest this year, but Project Blog has stepped in to fill the void. This is the event where bloggers blog for 24 hours for pledges for their favorite charities.
I did the Blogathon a couple of years ago, and it was an eye-opening project. There is the good that is done for the charities, and there is also the chance to meet new bloggers. If you have a chance, check some of them out.
I saw Kane's citation of Project Blog first, then Crayons and Playdoh's post.