Online resources for learning/practicing bridge
Here are some:


Richard Pavlicek's site on bridge which has puzzles, articles explaining concepts, bidding systems, calculators etc. A very good free resource.
The now discontinued deal of the week by Fred Gitelman which is an over the shoulder type of software. Free. 
Bridge Master and software by other world class players: http://bbi.bridgebase.com/cgi-bin/store/commerce.cgi (not free, but highly recommended).