Looks like your MySQL is taking all the power.
I've had the same, and after running the "MySQL Performance Tuning Primer Script" (and doing what it's suggesting) managed to tweak it better.
The script is coded by Matt Montgomery, who is part of a team that manages +7,000 linux servers!
The script can be found here: http://day32.com/MySQL/
Small note. After changing things in the my.cnf you will need to wait 48 hrs to see the "real" effect!