I use two fans in opposite corners of the stand. One blowing air in during the day, one blowing out at night:
http://www.jlaquatics.com/phpstore/s...t_ID=cv-sfan04
It also speeds up depending on temperature. I have very little temperature fluctuation using this method during the summer - and don't use a chiller. It maintains my pH and provides good airflow.
Before it was just a sweat camp in the sump area, this definitely improved everything overall. My sump area is also completely enclosed, with a plastic vinyl backing to prevent excess humidity in the room and evaporation. It keeps the evaporation down, and my windows don't sweat (as much.) if it were an open back.