I do security installs for a living and could recommend something for you. What sort of budget do you have? What do you want to get out of having such a system? Do you want to be able to record footage, or just view? If you want to record, how long do you want the images to be available before they are overwritten? Do you want to be able to connect remotely and view your cameras? What sort of detail are you looking for? Would an analogue picture be ok, or do you want something HD?
(I'm not trying to get business or anything, just wanted to let you know where I'm coming from)