Designers are not always masterful typographers and this includes the ability to perfectly match up interesting font choices.
The Type Genius webapp was made specifically for help with font matching. You can select from a number of very popular web typefaces and you’ll get a custom list of possible matches.
Some typefaces some with a few options, others just have one. The idea is to find a series of fonts that go well together in a heading/paragraph setup, or something similar that you’d find in a print design project.
The list includes a number of system defaults along with popular choices from the Typekit library and Google Webfonts.
If you’re stuck with a particular font pair-up I’d highly recommend Type Genius. The app is simple to use and delivers quality results every time.