Many sites cross the catagories I have listed below. Check them all out; if you find a dead or incorrect link please let me know.

Vendors

A to Z Hobbies
Aerocon
Aero Pack International
Aerotech
Aerospace Specialty Products
Al's Hobby Shop
Apogee Components
ARA Press
Belleville Wholesale Hobby
Blacksky
Booster Vision
BSD High Power Rocketry
Countdown Hobbies
Custom Rockets
Discount Rocketry
Estes Rockets
Flis Kits
Giant Leap Rocketry
GPSFlight - Advanced Long-Range Telemetry Solutions
Just Rockets
Launch Pad 2000 - Estes & Quest Rockets
LOC - Precision
Missile Works
Modern HPR Press
NARTS
NOW Hybrids
Newton's 3rd Rocketry
Pyramid Rocketry
Perfect Flight
Photos by Nadine
Public Missiles LLC
Q Modeling
Quest Aerospace
Rocketees
Rockets Away
Rouse-Tech
Semroc Astronautics Corporation
Shadow Aero
SpaceCAD
Sperachutes
Sunward Aerospace Ltd
The Squirrel Works
Thrustline Aerospace
Top Flight Recovery
Walston Retrieval Systems
Wildman Rocketry

Materials

Aerosleeves - High Performance Composite Sleeves
Balsa Machining Service
The Graphite Store
JimZ Rocket Plans
Kite Studio - Parachute Material
McMaster-Carr
Metal Express - Metal Cut to Length

Motors

Aerotech Hybrid Information
Animal Works
CP Technologies
Chemroc - Designing Rocket Motors
Firefox Enterprises - Chemicals for Motors
HyperTEK - The Easiest Access Of Them All!
Loki Reseach
Low Cost Rocket Fuel Pump
MB Rocketry's HPR-EXP site
RCS Rocket Motor Parts

Rocketry Organizations

Arizona High Power Rocketry Association
FITSTAR
Fly Rockets
Jamstars
NASSA HOME
National Association of Rocketry
Souther Arizona Rocketry Association
Superstition Spacemodeling Society
Tripoli Rocketry Association

Other Rocketry Websites

John Coker's Rocketry
Rocket Team Vatsaas - An Awesome Rocketry Site!