Tune Your Google Ad Campaign from Kevin Lee at ClickZ provides a lot of useful tips, especially for those who have not updated your adwords campagins for awhile. It can really make a difference in your campaign when you monitor and tweak your keywords.
Ive tweaked many clients Google Adword campaigns and it has always resulted in a substantial savings in money. Its important to have someone monitor the campaigns, especially if your bidding on expensive keywords or have multiple campaigns running.