Flickr groups of interest

http://www.flickr.com/groups/939803@N24/pool/

A mountain bike group for professional photograhpers, heaps of great actions shots.

http://www.mattstuart.com/

Not a flickr group but some extremely well time photos by Matt Stuart

http://www.flickr.com/groups/underwaterbw/pool/

Underwater photography in Black and White. An interesting spin on often vibrant and very blue underwater photography.