there are tons of variations on jumping and you should practice all of them.  Vertical height, horizontal distance, two feet, one foot, side to side.  you should be proficient in all modes of jumping.

You could try VerticalJumping.com. :-P

http://www.verticaljumping.com/lessons_from_parkour.html

Many of the same concepts for better broad jumps apply to better vertical jumps, so make sure you read this article well: http://parkourelements.com/body/2/broad-jump. Elements doesn't have a vertical jump guide...yet.

The article Nick Kelly posted is a good one to check out as well.

Arguably the most important thing is going to be just go out there and practice jumping. Experienced traceurs have done thousands of broad jumps but maybe only hundreds of vertical jumps, if that. And that is a main reason why many traceurs have fulfilled more of their broad jump potential than vertical jump potential.