TypeKit is great, I use it all the time. As far as a service that allows you to have web fonts on you’re website, in my opinion, they’re the leader. But there are other alternatives out there that give you access to more fonts then currently exist on TypeKit. Here are a couple:
I want to highlight Fontshop in particular. They have a pretty sweet plugin for Photoshop and Illustrator that allows you to “preview any of [their] 150,000+ fonts, in the context of your own artwork”. Why TypeKit hasn’t come out with this yet, considering that they’re now owned by Adobe, boggles my bind.