When I ordered my 550D I also ordered Understanding Exposure by Bryan Peterson. It came recommended by several people I know as a good refresher. I already knew the basics of photography having taken 5 years of photography in high school but that was a long time ago and only 2 classes a week. A lot has changed since then too.
My foundation was built on Pentax SLR film cameras. In high school we used the Pentax K1000 and when I showed great enthusiasm my parents gifted me a Pentax MZ50 for my 16th Birthday. This camera served me well, until recently when it died :( which prompted my DSLR purchase.
Understanding Exposure was indeed a great refresher on the principles of correct exposure photography. Having learnt to shoot manually in school and having a sound understanding of manual camera settings I found this book an easy read. He writes in quite a colloquial style which is so nice, not like a text book at all. I did pick up a few new tips, especially about metering in the right place.
It was an excellent place to start and i'm sure I will look at it time and time again.