This week Packt Publishing are offering a sweet deal on their PacktLib subscription service. You get access to over 3000 titles for $100 for a year.
I am a big fan of Packt, I think they release some quality books so a hundred quid is an excellent price.
If you are unsure have a look at some of my (or other's) reviews to get a feeling for their work. You can also have a look at their reader and see whatever books you already own to get a feel for the format.
Definitely worth checking out =)