For a practical (but involved) overview, there's this: http://webtypography.net/toc/

It's a classic typography book translated to a web context with the relevant CSS styles. Pretty cool.

For a more easily digestible (and interactive!) overview, the one that comes to mind is the Interactive Guide to Blog Typography: http://www.kaikkonendesign.fi/typography/

If you'd like to check out more resources, hackdesign, a newsletter of curated design-related links, is focusing on typography this month: http://hackdesign.org/courses/