Below are a few links that you may find useful.
PlanetCatfish - THE Aquarium catfish website
UK Aquarist Classifieds - A must for anyone based in the UK
Urban Philosophy - Perfect If you Live in the Netherlands, and need someone to feed your fish whilst you're on Holiday
Tropical Fishfinder - Based in the UK great deals and a useful resource
Aquarium Electrical Systems - Very informative
Scotcat - Another fantastic resource and of course, it's Scottish
www.l46.ch - Not in English but can be translated in Google
Fishaholics - A fantastic and very friendly site run by our very own Barbie!
Aquaauction - The UK's First Online Aquatic Auction Site
Corydorasworld - What else can I say!