Top 5 - stand up message forum (better than pwctoday)

Blowsion - My choice for aftermarket parts - The best stand-up vids on the web
Pacific Jetsports - Jetski boneyard

Wet Wolf - Jet pump performance - Awesome, innovative parts: hood seals, mixture screw knobs etc.
Factory Pipe - In my opinion the best pipes on the market.
Coffman Pipe
Riva Yamaha
R&D Performance
Solas - Impellers, pumps, and intake grates.
Skat-Trak - Impellers, pumps.
Pro-Tec - Yamaha and Polaris performance.
Wiseco Pistons - The only pistons I use
Pro-X Pistons
Umi - handling components
MSD Ignition - offers programmable ignition modules, enhancers, lightweight flywheels
Group K - Proffesional aftermarket high performance shop.
Jet Works - manufacturer of  performance parts and accessories.
Boyesen - Reed Valves and stuffers.
CarbonTech - Reeds
Jettrim - bitchin stitchin
24/7 Innovations - Graphics
Exotic Signs - Graphics
SpeedWerx - Many Go-Fast parts for Yamaha and Kawasaki.
Wavetech - Site is currently down, check back
Dennis Kirk - Located in Minnesota, offers thousands of parts. Also has scratch/dent warehouse. Check Ebay.

General Web Pages - high traffic message boards  (not as good as x-h2o) - message board, great classifieds section, good all-around site. - aftermarket store - excellent customer service

Enthusiast Sites
Eric Malone's Homepage
Scott Hayne

Used Jet Skis/Parts
Pacific Jetsports - Jetski boneyard
Boat Trader - Updated daily, tons of jetskis for sale.
Classifieds - Link to the classifieds section @

Performance Information
George Grabowski - Jetski performance info. - Parts, Services, and Performance Tips