I noticed that I would often place direct ad sales on various parts of my webpage and then I would forget when to take them down since I had so many. I then thought of simply using Google Calendar to manage my ads.
Whenever I place an ad, I simply create an event in my calendar that is scheduled for the end date of duration of the ad, and in the description I describe what it is, where I put it, and the contact information of who bought the ad. Under the options when you are creating the event, I have Google sent me an email 2 days before the event, so I can contact the advertiser for renewal. It is as simple as that.
With a combination of Google Calendar to manage my ads, and Gmail to get notified and to contact advertisers, it is a perfect combination for managing advertisements.