Gang of Four!!!!
Heard about them, yep great book to read and educate yourself if you are into Writing reusable code and patternizing them, Dont forget there is also Anti Patterns. However reading that book could be quiet an effort but if you need quick reference and get your job done I would recommend this website
http://home.earthlink.net/~huston2/dp/patterns.html
The short notes, illustrations in C++ and java is great, I learnt a great deal good ahead knock yourselves out folks.
