They've always told me "Some of the best things in life are free". Back then, it didnt make a lot of sense, but over the years i've found this to be true. Though i see internet as the best thing thats free, there are a few little things that fall into that category of "best, but free" as well.
One such thing is the book by Mark Pilgrim Dive Into Python. In short, it is one of the best of its kind book on the programming language - Python. And secondly - its free ! Check out marks blog "Dive into mark" for more details.
The book can be ordered in hard copy or freely downloaded in various formats (html, pdf, word document, text, docbook, etc). from here. Translations in several language exist.