If you still want one check out Simply Safe, I believe after you purchase your system, it is only $15/mo and no contract. I have a friend that has them and they have been happy.
We have ADT, while they service is nice, I realized I signed up for a 3 year contract, I thought it was a 2 year, we are trying to sell the house and if it sell and the new owners get signed up within 60 days, then we are let off the hook, but if they don't we have to pay that last year, Grrrr