It's always horrible to have to go through a booking agency because of all the extras they want in order to give you the right to purchase a ticket. For that reason and wherever possible, I've always gone directly to the venue's own Booking Office. As Bigdog has already mentioned, DeMontfort charge £1.00 Admin fee (total irrespective of the numeber of tix bought) for a credit card payment (nothing for using a debit card) and £1.00 to post the tix - very quickly too.
I'm going to Poland in January to see the band in Katoiwice and used Eventim to buy my tickets - again, a small admin and postage fee and fantastic swift and efficient service - I even got to choose which seats I wanted.
I think Ticketbastards are the ultimate rip off merchants. A charge for every ticket bought and an array of additional charges for postage etc. They generally don't even offer the best seats available (Steve, We're sat behind you in row 2 next May!!!).
I appreciate that agents are needed, but their reputation would only be enhanced if they dropped their charges to an acceptable level - greed is not always good.
On that matter, do any of the ticket agencies sponsor or promote any of the shows they sell for?