Welcome to the forums!
Die hard's will say your local library. Young fanatics will say ellusionist, theory 11 and penguin. They're both right. Once you get in the Swing of things you will learn magic from all sources and realise they all have their pro's and cons. Ill say, Mark wilson's complete course in magic. It's a great starting point, and it's cheap. Head to your local library and see if they have any books, once you decide what types of magic you would like to perform, you can progress to the downloads or more books. I wont point you towards downloads today because for the price of most downloads you can buy mark wilsons book! Also, if you were to buy the latest card trick released on your first day in magic, you might find that cards just aren't your thing. Learn something from each type of magic with the help of that book. You'll learn very quickly what is for you and what isn't. The forums will help you in every way you can imagine.
Good luck!