The Feeling Good Handbook by David D Burns, MD is a good book on CBT. It has some good techniques to help you think of replacement thoughts for the negative. I sometimes draft other people into my pursuit too. I find that if two or three people tell me that its okey to not finish all my work asignments, I get it faster. I hope it works on other negative thinking patterns.
Mood Gym which is a cool website based on Rational Emotive Therapy and CBT. I think there is an old link to it in psychotherapy that is titled free T. It has some thinking techniques to help one to re-think things.