I have the Introduction to Algorithms book. It's pretty darn good. The
   usual material for universities around the world.
   If your nation's laws permit it you may consider downloading a full
   copy for free. In The Netherlands it is legal, as making a copy for
   user at home is legal.
   Take care not to use something like [1]torrentz.eu though, torrents are
   also uploading and thus illegal in NL. You might instead consider using
   Google.
   A quick search for "introduction to algorithms +.pdf" finds us:
   [2]http://ldc.usb.ve/~xiomara/ci2525/ALG_3rd.pdf
   [3]http://www.slideshare.net/hiepkhach_1006/introduction-to-algorithms-
   3rd-edition-thomas-h-cormen-charles-e-leiserson-ronald-l-rivest-cliffor
   d-stein
   and
   [4]http://cs.gzu.edu.cn/lab/upload/cont/%E8%B5%84%E6%96%99%E4%B8%AD%E5%
   BF%83/%E7%AE%97%E6%B3%95%E5%AF%BC%E8%AE%BA.pdf
   And it works for just about every good book out there.
   Of course, use it only legally! It is important that publisher's rights
   are respected. As a community we come to find the optimal set of rules
   through our well designed systems of consent. If law follows from it,
   it must be respected.

References

   1. http://torrentz.eu/
   2. http://ldc.usb.ve/~xiomara/ci2525/ALG_3rd.pdf
   3. http://www.slideshare.net/hiepkhach_1006/introduction-to-algorithms-3rd-edition-thomas-h-cormen-charles-e-leiserson-ronald-l-rivest-clifford-stein
   4. http://cs.gzu.edu.cn/lab/upload/cont/资料中心/算法导论.pdf