Urban Freeflow
Great descriptions of some of the basic moves from the UF team.

Levity
Great descriptions of some of the basic moves from the Levity group.

Best and Worst Exercises for Bad Knees
An article at prevention.com outlining what exercises you should and shouldn't do if you have problem knees. The goal is to strengthen the muscles surrounding the knee to reduce stress on the joint.

Knee Stretches
Set of stretches for people with bad knees.

parkour.net
Most central site for parkour currently.

leparkour.ca
Canadian Parkour Association, find people to train with in your area.

pkto.ca
Parkour Toronto. Portal for Southern Ontario Parkour communities.

pkcc.ca
Parkour Network for Canada's Capital. Portal for the Ottawa Parkour community.

pk514.com
Parkour Montreal. Portal for the Montreal Parkour community.

David Belle.com
Homepage of the creator of Parkour: David Belle.

foucan.com
Homepage of the co-creator of Parkour: Sebastien Foucan.

Worldwide Jam Magazine
The first ever Parkour magazine, has articles and a forum.