I found two useful links that talk about dealing with negative people.
The first is 3 brief points that really make you think about letting go and getting out of the idiots ball court (regaining perspective and focus). Even though its focused in a customer service platform, the tips are so simple and useful that they could be applied anywhere. 3 Powerful Secrets For Dealing With Negative People by Peter Murphy
The second is a book. I read the intro and could relate already. It started off with a few surveys that I quickly skipped but appeared very useful…. hey and its a freebie.