Professional types...

AS & A Go-Skate - skate park schemes
Bendcrete Ramps
Clever Curves
eibe ramps
Evolution
GBH Ramps
Huna Designs
Rampage
Sk8ramp
Vertical
Wup Doodle

Build your own...

Buildaramp.com
Heckler mag
Rail Building Tips
Ramp FAQ
Skatelite Ramp Surface
Toxboe SkatePark - Blueprints for Skate Ramps