Typecast (in beta at the time of this filming) is a really neat web app for playing with web typography. It gives you a great interface for playing around with the basics of typography, like what your headers and body copy look like. The real fundamentals: sizing, line-height, coloring, all that stuff.
What makes Typecast really cool is that you can use all sorts of custom fonts within it. We're using Typekit in our project so far, and all those fonts are available. But they don't just have Typekit fonts available, they have fonts from FontDeck, Fonts.com, and more.
When it comes time to deploy, you're on your own as far as actually setting up those fonts, but you can play with them from with Typecast all you like.
We play around with a baseline grid and I share some thoughts about that. We also play around with a couple of different header fonts, body fonts, and some playful fonts.