Changing Fonts

You can use a mod to change in game fonts. Or you can replace the original game fonts with the fonts you want to use. Create the following folder:
Classic WoW: <WoW directory>\_classic_\Fonts\
Retail WoW: <WoW directory>\_retail_\Fonts\
Create copies of the font file of your choice, place them in the above folder, and rename them to the following names:
FRIZQT__.ttf (the main UI font - NPC names, player names, spell names, item names, buffs, quest log text, combat text, button text)
ARIALN.ttf (chat font, info text, small text)
skurri.ttf (default unit frame combat text)
MORPHEUS.ttf (mail text, quest log header text)
FRIENDS.ttf (friends list text)

Popular Fonts

Andika Basic, Alte Haas Grotesk, Comfortaa, Expressway Free, PT Sans Narrow, Roboto, SD Fresh Regular, SF New Republic, Tork
dafont has many good fonts to choose from.