Audiophile

Balanced Audio Technology
http://www.scottwalkeraudio.com/
Synergistic Research Acoustic Systems at Scott Walker Audio

Camping and Survival

http://survivalkitmarket.com/.

Guitars

Wooden Wizard Guitars

http://www.woodenwizardguitars.com/
 

Guitar Accessories

Effectrode
http://www.effectrode.com
Cool tube based guitar effects!

Jet Slide
http://www.jetslide.com/index.shtml

Guitar Amp Kits

Guytronix Vacuum Tube Amplifier Kits
http://www.guytronix.com/pages/1/index.htm
No clones here. Unique tone machines designed by Gary Gerhart

Guitar Amp Repair

Aeriel Amplification (Australia)
http://www.aerielamplification.com.au/

Viking Amplifiers (Virginia USA)
http://www.vikingamps.com/

Guitar Amp Stuff

How to bias a Fender Hot Rod Deluxe or Deville
http://studentweb.eku.edu/justin_holton/bias.html

Scumback Speakers
www.scumbackspeakers.com

Tonequest Report
http://www.tonequest.com/
This site is a MUST for guitar player/tone sluts. Great articles on guitars, amps, tubes (by yours truly) and all aspects of achieving nirvana in guitar tone. Check out the premier issue on line and ask David for a free copy. Don't forget to tell him I sent ya!

Weber VST Speakers, amp parts, bias probes
http://www.webervst.com
Manufacturers of vintage style loudspeakers and other products for the vintage equipment enthusiast. Great guitar/amp/tube discussion boards too! Good source for BIAS PROBES.

Guitar Amps

Peden's Vintage

www.pedensvintage.com/index/Home.html

Viking Amplifiers
http://www.vikingamps.com/
Very nice guitar amps. Original designs, no clones or kit amps. Check out the Pillager. Smokin' amp with the best overdrive channel I've heard. Here's a review

Guitar/Amp Forums

Fender Forum
http://www.fenderforum.com
Forum for the discussion of anything to do with Fender guitars and amps. Great technical discussions on Fender amps.

The Gear Page
http://www.thegearpage.net/board/
If you're a guitar/amp/tone freak, this board is for you!

Unofficial Univalve Page
http://www.univalve.net/forums_new/
Great resource for THD amp users. Lots of tube reviews and discussions.

Tube FAQ

Justin Holton Vacuum Tube FAQ
http://studentweb.eku.edu/justin_holton/tubes.html
Great reading for the tube enthusiast!

Tubes 101: What Every Guitar Player Should Know About NOS Tubes
http://www.tonequest.com/articles/article3.htm
Tonequest article by yours truly about tubes. It's a bit dated (especially the prices)but very relevant as a primer on amplifier tubes.