Tim, a big question to ask yourself is what type of system do you want to use? CCTV or IP Based? CCTV requires that you run coax cable with BNC connectors to all locations. The initial hardware is much cheaper and is easier to get into because they are a dime a dozen on cameras and such, but the problem is getting coax to all locations.
I have a bunch of Linksys Wireless IP based cameras around the house (1 looking out the back via a 2nd story window, 1 out the front via 2nd story window, 1 in the garage, 1 in the shop) and they work well. Most IP based ones don't do well outdoors unless you get the high end Axis cameras. I like the IP based ones as I can get to them remotely very easily via iphone/android/etc. Linksys has software that runs on Windows computers that acts as a DVR.
Most of the time you want to have a pan/tilt camera on your yards, things like a garage or shop camera don't need to be, but outdoors should usually be pan/tilt. I've used this one up at the parents cabin and it works well: