Todd's Lowrider Page - He has lots pictures and some great info on hydraulics.
True Ambition - a great story of turning a factory GMC Sonoma into a smooth-riding ground scraper. Nice website design too!
If you are in the market for hydros, check out Prohopper.com to see if you can really afford it! =)
Here's the Yahoo category for "lowriders" for tons more related links.
Lowrider.com - need I say more?
Lowrider Magazine - The one, the only!
Hot Rods, Etc - a nice page of lowrider/classic/hot rod pictures (the "flaming exhaust" section has to be my favorite!)
The BumpStop - the best organized showcase of cool cars on the world wide web!
Low Life Customs - Canadian lowrider club, sporting a picture gallery with all types of ground scrapers!
UK Yanks - a cool club in England for lovers of American cars.
Unity Lowrider Car Club - another group that originates in the UNited Kingdom; check out their "Member Rides" section to see how the lowriders differ from those in America!