I love read-a-thons :)! The reason being is that I am very competitive!! So naturally they are a good fit for me and I have signed up for a few that are coming up. They also help reduce my TBR pile that is just sitting on the floor by my nightstand.
The 2011 Spooktacular October Paranormal Reading Challenge (10/1 - 10/31)
The Inheritance Cycle Re-Reading Challenge (10/18 - 11/8)
Wrapping Up 2011 Read-A-Thon (12/22/11 - 1/1/12)
So those are the ones that I have plan to do at the moment; I'm sure that if I stumble across another one that I will most likely join it as well :)