About 8 years ago when I opened my shop I purchased a security camera kit from Sam's club. It cost me around $1200, and didn't seem to be that great in the long run. I only bought it in a hurry because I was about to leave for Vegas for a week. One day, Christmas morning around 8am actually someone threw a brick through the windows and stole some items and ran. The footage wasn't good enough for the cops to identify him with, even though I knew who did it because he walks by everyday with the same coat on.
So none the less, I continued to use this outdated system, until I had this idea. HD webcams. The local staples were having a sale/clearance on the Microsoft HD webcams (originally $100/ now $35) so I grabbed as many as they had.
then I downloaded the free/open source software ispy http://www.ispyconnect.com/
With it I can set it to record on motion, when to record and anything you can think of and it doesn't just work with only webcams, it works with all kinds. I chose webcams because they have a nice picture and they're cheap. This software supports up to 16 cameras, and it can also record sound.
I have this hooked up to my computer in my back office and it's running 24x7. if the computer reboots, the software loads back up as well and hides in the systray. Not only can I catch someone breaking in, but it can come in handy just in case someone says you didn't tell them something (microphone will prove that wrong) or if they claim something like you never gave them back their laptop charger. There are a lot of scenarios i'm sure.
I think some of the plus sides of having the webcams are they're small and easily hidden, they use usb ports (hello usb hub) and they're relatively inexpensive. I also heard that Western Digital has now a "Purple" series hard drive that is designed for video surveillance. Although I've been using my WD 750GB black edition and it's been doing great for the past year now, and the storage space seems to be a great amount since I don't keep anything older than 90 days they way I have it setup.
If you want to know more detail about how I have it setup, including my motion sensor lights for nighttime visibility, just reply to this post or send me a pm.