When making a character sheet/developing a character -
height/weight image chart
names that mean '___'
(nationality) names
(nationality) surnames

When developing a world - 
Ancient Egypt/Rome/China // Middle Ages Europe/England/Scandinavia


For recent RPs -
Mongols
Celts
Women warriors
'___' synonym (often followed by a synonym for the synonym.)
wtf how do I spell '___'?
Ancient Egyptian Fashion

etc, etc.

But mostly, I use it for spell check because oh my god, I cannot spell worth a damn. Sometimes I get close enough for my browser or word program to guess, and sometimes I need to use google to figure it out. xD