Online resources:

* [The Catsters channel][1]
* [MATH198 course notes][2] - examples in Haskell
* [Rydehard, Burstall: Computional Category Theory][3] - examples in ML
* [MAGIC course][4]
* [Barr, Wells: Category theory for computing science][5]
* [Jaap van Oosten: basic category theory][6]
* [Tom Leinster][7]
* [Eugenia Cheng][8]
* [Steve Awodey][9] - very similar to the book mentioned by Quadrescence
* [Daniele Turi][10]
* [Thomas Streicher][11]

Books:

* "Basic category theory for computer scientists" by Benjamin Pierce
* MacLane - solid mathematical foundations, but hardly any references to computing
* [Abstract and concrete categories][12] - might be considered too verbose, but it's full of examples

Category theory in Haskell:

* [Wikibooks introductory text][13]
* [sigfpe's blog][14] has a lot of category theory articles - (di)natural transformations, monads, Yoneda lemma...
* [Comonad.Reader][15]
* [The Monad.Reader][16] - check "Calculating monads with category theory"

[Another list][17]


  [1]:http://www.youtube.com/user/TheCatsters
  [2]:http://haskell.org/haskellwiki/User:Michiexile/MATH198
  [3]:http://www.cs.manchester.ac.uk/~david/categories/book/book.pdf
  [4]:http://www.cs.manchester.ac.uk/~hsimmons/MAGIC-CATS/magic-cats.html
  [5]:http://www.cwru.edu/artsci/math/wells/pub/ctcs.html
  [6]:http://www.itu.dk/~birkedal/teaching/category-theory-Fall-2001/basiccat.ps.gz
  [7]:http://www.maths.gla.ac.uk/~tl/ct/
  [8]:http://cheng.staff.shef.ac.uk/catnotes/categorynotes-cheng.pdf
  [9]:http://www.andrew.cmu.edu/course/80-413-713/notes/
  [10]:http://www.dcs.ed.ac.uk/home/dt/CT/
  [11]: http://www.mathematik.tu-darmstadt.de/~streicher/CTCL.pdf
  [12]: http://katmat.math.uni-bremen.de/acc/
  [13]:http://en.wikibooks.org/wiki/Haskell/Category_theory
  [14]:http://blog.sigfpe.com
  [15]:http://comonad.com/reader/
  [16]:http://www.haskell.org/sitewiki/images/8/85/TMR-Issue13.pdf
  [17]: http://www.cs.le.ac.uk/people/akurz/books.html