I've been thinking about doing this for a while. I just got a NAS that will work as a controller and recorder for the cameras. Highly recommend any Synology NAS, but I understand the camera station still needs some work. They'll get it right soon, I suspect.
Cameras are a lot tougher. You can get some wireless ones, but they frame rates can be really bad as well as the quality (like 640x480 type output). I wish my house had been wired with ethernet cables everywhere, but it wasn't which means connecting cameras becomes a task. I set something crude up at my last house that used wireless bridges but they tended to drop out a lot.
I found this recently which looks really useful.
Wireless w/ POE There are other items out there like this (last I looked, there was only one). With this, you could plug it in in the garage and then run a long cat5e cable outside (they make outdoor ethernet cable) and make for some pretty easy placements.
*edit* I guess I didn't complete that thought. You would then buy a POE camera and the power for that camera would be supplied from the ethernet cable and you wouldn't need any extra power wherever you want to place the camera. One small hole that you would fill with weatherproofing through an eve in the garage to outside and you have a remote camera ready to go.