That being said, my hands-down, top resource for webfonts is Google Fonts. Why? Because Google makes it crazy easy to use their fonts on your site. If your theme doesn't already have settings for Google Fonts (which is probably does) all you need to do is add a line of code to your header and then style your CSS. That's is. Super duper easy. So easy a caveman could do it-esque easy.
What's more, Google Fonts has a pretty big selection of fonts, and I'm going to keep it real when I say:
As a website DIYer, if you can't find fonts that "work" for you on Google Fonts, you are probably trying way too hard.
If you're unsure what fonts are best for your site, I encourage you to sort Google Fonts by popularity.
Sorting by popularity means that you can see what a massive subset of web developers/Google font users find to be the best for the web. Open Sans, PT Sans, Droid Serif -- it's not surprise these are top choices because they look great on the web.
When it comes to selecting commercial fonts to use in other elements of your branding, I highly suggest checking out:
If you're looking for more free fonts that are almost are good as commercial fonts, check out FontSquirrel.