I recommend for a first reading on category theory:

[Martin Brandenburg, Einführung in die Kategorientheorie][1]

It is really an excellent exposition with some nice perspectives on the concepts,<br>
supported by plenty of examples. :)

(Note that it is provided in German only.)

A lot of thanks to Konrad S. for suggesting to me the reference!<br>
(Such a pity, that I just missed the chance to meet the author in person..)



  [1]: http://www.springer.com/de/book/9783662470688