Fonts.com

Fonts.com is the biggest typographic marketplace on the planet. Owned by Monotype, it offers more than 150,000 desktop and web font products for you to preview, purchase and download. You can also learn about new typeface releases and discover typographic tips and techniques.
There are a number of reasonably priced subscription plans for web fonts, starting off with a free package if you have very low traffic or just wish to try the service out.