How much ram do you have?
Is your server optimized, or are you simply throwing all the hardware it can contain at it?
Try
Make a my.cnf backup before doing
Code:
cp /etc/my.cnf /etc/my.cnf.prev
Then change following values on /etc/my.cnf to
Code:
max_connections=500
wait_timeout = 30
query_cache_limit=2M
query_cache_size=24M
Restart mysql.
Code:
service mysqld restart
This should help