I like to spend my time wisely (not really but it sounds good) so I try to combine two of my hobbies, photography and diving together to do underwater photography :-)
There is lots of info out there on the web. But there is one particular very nice online magazine called Underwater Photography . It has many beautiful photos (even for non-divers!) and items on material and many tips/tricks. (no, i'm not getting anything to say that).
btw. above picture was taken by me last year in one of the dutch lakes ;-)