Best Extensive Betta Sites:
These web sites include information on many aspects of betta keeping.
NippyFish, A Betta Blog <---- this is actually a blog but it covers everything. Just search by keyword and you'll come up with tons of results.
http://www.nippyfish.net/ <--a different betta site not related to the blog above
http://www.ultimatebettas.com/ <---this site has forums where you can ask questions and talk with other betta keepers.
Yahoo! Answers Fish <--- I can't tell you how many betta questions I've had answered here. Many people have had similar questions to yours and I bet you find what you're looking without even asking a question.
Wayne Schmidt's Betta Pages <--all kinds of quirky things about bettas as well as basic care
Other Neat Sites:
Betta Growth in Pictures <--a scaled look at betta growth through eleven weeks old
Best Betta Supply Stores and Sites:
These chain stores and online stores have most if not all of the supplies that you will ever need for betta keeping.
API <-- even carries a line of betta products
Doctors Foster and Smith <--also carries API products
Bizrate Fish Supplies <--all kinds of betta products...some of the bowls are a little small, though.