Caving Supplies: A good website for those in the United Kingdom. Big selection
Karst Sports: A dealer in the United States. Great selection and prices.
Bob and Bob Equipment: Some basic supplies.
Organizations
National Speliological Society: If you want to go caving, this is the place to join. For a few bucks a year, you can become a member, join a grotto, and get to go on a bunch of caving trips. Look on the page and find a grotto near you.
York Grotto: This page is for the grotto of York Pennsylvania. They take many fun trips according to their site, Wish I was there sometimes so I could go too.
Timpanogos Grotto: This grotto is my nearby grotto. I want to join but the $30 or so a year seems high, considering that very few grotto trips take place at 6:00 AM on a weekday.
Bucks County Grotto: Another PA group. Fun Pictures.
Personal Pages
These are a few pages about caving from some people on the internet. They tend to be from Pennsylvania or Utah.
Matt Satlzer's Website: This website deals with caving in Pennsylvania, mainly in the southeastern portion.