CustomCombatText is a very simple and lightweight addon to let you change the font of blizzards default floating combat text.
How to: find a font you like, say at Dafont.com, download it and change its name into font.ttf (must be ttf format)
Exchange it with the one in the CustomCombatText folder.
Install: as any normal addon. Download the ZIP and extract the CustomCombatText folder into
World of Warcraft/interface/addons
Default location= C:\Program files\World of Warcraft\Interface\AddOns