For you engineers, scientists and architects, I highly recommend Dr. Judy Wood's book Where Did The Towers Go?

I greatly enjoyed her book, which is of college text book quality, where she has collected some fascinating evidence and analysis related to 9/11. It's the most sensible investigation of what happened to the buildings and people in NYC on 9/11 that I've seen so far, and I've looked at many theories, investigations and opinions that have been offered to date.

She has some videos too, most of which I haven't had time to watch yet.