If you like Python, check out How To Think Like A Computer Scientist (http://interactivepython.org). It's aimed at introductory CS classes, but the inline interactivity is pretty cool! (Shameless plug: a couple of my professors developed this, and I spent last summer contributing to it).
For those who don't like Python, and want to think like a real computer scientist check out Interactive SICP (http://xuanji.appspot.com/isicp/)
It is also aimed at introductory CS classes.
