Typography can make or break a design. Up until recently, if you were working for the web, you had to rely on font-stacks, SiFR or @font-face conversions that might get you sued. And it might still look rubbish on your computer.
Luckily things have changed now. Here are some resources for getting your head around typography.
In comparison to this, the Elements of Typographic Style as Applied to the Web does look a little dated. Still, it’s a solid resource (and based on a lauded book of a similar name for print).
While there are some terrible free typefaces in the Google Fonts repository, there are some beautiful ones. Luckily, A Beautiful Type picks those ones and the best combinations and shows you with, er, beautiful examples.
And, if you’re hard-core, I recommend looking at the My Fonts newsletter for information on typefaces and even interviews with type designers.