I'm not sure, now, how I came across this sport/exercise, but I've become temporarily obsessed. Here is some information about parkour, and links to other sites and videos.

Parkour was invented by David Belle, influenced in part by his father, who was a soldier, and also by the "Natural Method of Physical Culture" developed in the early 1900s by George H�bert. The information on H�bert is very interesting--to me, as interesting as parkour.

Parkour emphasises getting from point A to B by effeciently overcoming obstacles. Instead of walking around a fence, a traceur would vault it. Faced with a low wall, he would jump and scale it. Rolls are emphasized in order to reduce joint injury. There is a definite simian quality to the movements. At its best, parkour is fluid and strong. These fellows (and a few ladies) are in excellent condition.

There are two branches of parkour. One is the "pure" form, which is my opinionated way of saying it's the form approved of by David Belle. Effeciency and elegence are emphasized, and extraneous movement avoided. If a motion isn't necessary to overcoming the obstacle, then it isn't parkour. The second branch was developed by Belle's friend S�bastian Foucan and is commonly called free running. In free running, obstacles are overcome, but style and art of movement are encouranged. Free running has more flips and other flashy techniques. While there's a wow factor to free running, I much prefer the simple grace of parkour. The most breathtaking element in parkour is the building leaps, and yet Belle doesn't treat them as overly important.

It's tough to find really good video, but here are some that I think properly reveal this interesting sport.

I think this is the best video. It shows off parkour, and is one of the few videos to remark on the danger of the sport, including deaths. (It's also in german with subtitles)
Parkour Pro7

A commercial that featured David Belle, and brought attention to parkour.
Rush-Hour (BBC)

A clip from the film Banlieue 13. Again, David Belle. (I could do without the scree-scree soundtrack.)

Another german television special. No subtitles.
Parkour on kabel1

Finally, a better view of parkour "training". This is nice, showing off lots of seemingly simple movements that are in fact difficult. For example, notice how Blane moves up and down the tree branches. also, check out the jumps from hand rails to hand rails. (And, sigh, why the harsh music for such a smooth sport?)
Blane - Power is Nothing Without Control

Near the bottom of this page is a list of videos that are supposed to represent good parkour.
Parkour News