We should really have a whole Tower of the Hand thread. The site is amazing. I've read so many theories that whizzed right by my head on there, which has made the whole series a lot more interesting to me. Plus, with the references and summaries for each chapter, I don't know how people read ASOIAF without it.
This was my biggest motivation to read the books as fast as I could. I hated not being able to click something for fear of being spoiled.
Re-read the Mockingbird essays a few days ago. Great stuff. Although I'm putting too much time into this crap
Loved this website ever since I found it after ACOK. Been great for doing my thread, especially if I read at night and post the next morning. Nice to just have that in case I forgot something.
westeros.org is really good as well. they have a great wiki and the Citadel section is a great resource for difference unanswered questions and "so spake martin" is a collection of pretty much every word GRRM has ever said about the series.