Puzzle Algorithms

topcoder's algorithm tutorials have been a great place to learn from.
esp the one based on geometry are good. here is the link
http://www.topcoder.com/tc?module=Static&d1=tutorials&d2=alg_index


apart from this, http://www.techinterview.org/index.html
claims to have some puzzles and algorithms frequently asked in tech interviews.

SPOJ

good place to start ones habit of SPOJing.
http://ajayfromiiit.wordpress.com/2006/06/04/spoj-method-to-solve-for-beginners-part-1/