I've subscribed to O'Rielly's Safari Bookshelf for a few years now (George has, too), but I was always disappointed that possibly their best series of books was not included: The Head First series.
If you want to effectively learn a new programming technology, nothing comes close to the Head First books. George recently completed the HTML and CSS book ,and I'm interested in the Ajax one.
I just read a post over at the O'Reilly Radar blog that these books have been added to Safari! For a minimum subscription of $9.99, you can have access to all of them. You can try the Safari Online Bookshelf for free for two weeks.