Auction Undercut Notifications
A feature that would check hourly to see if anyone has undercut my auctions, and then notify via e-mail. Assuming the APi data provides a player name with each auction, and the TSM users input their player names they wish to monitor, this could be a quick and easy addition to the TSM premium package.
P.S. - I would volunteer my PHP/mysql abilities if that would be at all helpful / if there's any interest in this idea.