Open-source fonts
I am a fan of open-source software since forever. Lately, while looking at fonts for a website, I've again come across open-source fonts. The main reason I like them is that open licenses leave no doubt about where and how you can use a font: personal projects, commercial projects, desktop applications, websites, and so on – which are instead usually limited with commercial licenses.
Do open-source fonts have to look unprofessional? Not at all. The League of Moveable Type has a great manifesto that explains why open-sourcing fonts is a good idea, and they offer some very good-looking fonts too; in fact, I still use the very popular Raleway, and for a while I've been quite in love with the less popular, futuristic-looking Orbitron.
There are many resources where to find, try, and download open-source fonts: