Rider Waite book

Tarot History Symbolism and Divination by Robert Place - IMO, one of the best you could possibly find on the Tarot in general.

78 Degrees of Wisdom by Rachel Pollack - Although I will say a lot of it is "her opinion", and it tends to be a bit dry and drags at certain parts. But it's a good book nevertheless, and one I think almost every tarot reader who reads with the RWS deck should read at least once.

the best book in my opinion...

Mastering the Tarot by Eden Gray, it gives you the meanings of each of the cards(minor and major arcana) and describes all of the symbolism and has practice readings and a lot more. You can find it in amazon.

gudrunn

I agree with gudrunn , Mastering the Tarot by Eden Gray is perfect, also in Spanish! is very easy to use, and explanations are easy to apply but deep.
Hope it helps!

I'm another fan of Eden Gray, I think she has a very good way of looking at the RWS deck and it's symbolism. Although Mastering the Tarot may seem dated to some, I think it still holds up very well. The Complete Guide to the Tarot is another one of hers that I'd reccommend as well. The Tarot Revealed was the weakest of her 3 books on the subject, it doesn't go into as much detail, and probably was the first book on the subject she published.

Of course the grand daddy of the them all is AE Waite's The Pictorial Key To The Tarot, which was the original guide book for the deck. It's on my reading pile and it is readily available and on my reading pile in fact.