Crowd Seats has launch to provide daily deal crowd sourced buying for sporting events. Their deals on tickets result in a 50-90% discount off face value and there are no ticketing fees. Once you purchase a ticket you will be able to print the voucher and bring it to the ticketing booth or will call to receive your ticket.
Currently the deals are available in Boston, Los Angeles, San Francisco, Chicago, and New York. They plan to offer tickets for MLB, NHL, NFL, NBA, and many other including colleges and local teams. It may take a while for the service to gain traction, and I would think many of the tickets that would be offered are ones left over when nearing the event.
This is an interesting take on the group buying phenomena that could disrupt the current model. You can sign up here, and join them on Facebook or Twitter.