If you are on Firefox, then install Firebug and the next time you see a well-designed site with a font you like, pop Firebug open and checked font-family under

If you are on Firefox, then install Firebug and the next time you see a well-designed site with a font you like, pop Firebug open and checked font-family under Computed Style for the text in question. Chrome/Webkit has a built-in "Inspect element" functionality that gives a similar access to the computed font-family value.