I've set up a number of my own, basically just a section of "ads" that display on a page either randomly, or with basic requirements (ie. category for that page etc). I've got records with an expiry date, so they automatically do not get included if the date range isn't appropriate etc.
I'd be interested to know what else you would like to achieve. I've got a basic plugin that checks a date field each day and sends me a list of any records past that date - this could be easily modified to send a list of expired, or so to expire ads..?
Cheers,
Tim (toledoh.com.au)