Full disclosure: I've been an alarm monitoring operator for 5 or so years now. I don't live in the US, I don't work for a company that operates in the US, so I have no way to financially benefit from helping the majority of /. users. The stuff I mention here I know well, but one thing I haven't a clue about is the home automation side of things.

Deterrants:

Large work boots, leaving lights on and such are helpful deterrants. Security stickers help, but no so much as most houses have them. A good idea that I didn't see mentioned in the comments, if you're not keen on getting an alarm is to get just the external siren of the alarm and stick that on the outside of the house. Don't get one of the metal ones, get one of the polycarbonate / plastic ones instead. No reputable companies have used the metal ones for years now, and a lot of burglars seem to know this. Again things like fences & dogs are also excellent deterrants. Although fences can act as cover so a burglar can muck around all they like trying to get a window open, without being noticed by neighbours.

Alarms:

I've encountered heaps of attempted break ins throughout my career. The vast majority of burglars will freak out and run once they hear a very loud siren screaming at them. Most of them get so scared by it that they drop everything in the process. If I had to put a number on it, I'd say this is what happens about 90% of the time. Even though it's far from a guarentee that you'll stop them in their tracks, it does make an excellent deterrent. I'd avoid the off the shelf junk you get from electronics stores and the likes, as they're usually total garbage. They're always either unstable, don't live long enough to be worth it, don't detect when someone does get into the house, or they drive the neighbours nuts false activating. You can buy a good, high quality unit from fleabay if you're feeling adventurous. I don't know how big your house is, but if you don't think you'll require more then 7 sensors now or in the future, the Bosch Solution 880 is a good buy and I see them frequently on eBay for cheap in a kit. You'll require some basic knowledge of electronics like being able to read some basic "this is how you wire this" diagrams in the install manual, and some basic DIY skills. It's a fairly easy system to install though, some of them are very hard for those who haven't got experience specifically with alarms. If you want something bigger / different set of requirements then email me (via bahamut.kicks-ass.org/contact/ - sorry but work know my email and I'd rather they didn't find this via google) and I'll let you know of something suitable.

I would avoid wireless sensors & remotes. Remotes not so much, but sensors definately. Interferance from aircraft, scaffolds, trees that cause RF interference whenever it rains, crappy light switches, aircraft, and a bunch of other obscenely weird stuff can all cause problems. It's not that common, but it does happen.

If you do buy a kit make sure it includes the panel (pcb, transformer & the case), battery, a couple of wired sensors, a keypad, a peizo / internal siren & a plastic / polycarbonate external siren (the one with the light) & CABLE! A lot of traders won't mention anything about the lack of cable in the ad, leaving you kind of screwed. Another thing I see them do is say "we'll install it for you if it's too hard" - be careful of that, they'll often way overcharge on labour to make up for the rock bottom cost of the hardware. I've seen them dump the install manuals that come with the alarm, and replace it with their own much crappier version so that it's more likely that they come crying for help. Most alarm manuals you can get online fairly easily though. Stay away from used alarms on ebay, they're almost always FUBAR'ed.

Alarm Monitoring:

This can be somewhat of a waste of time and money. Monitoring is often cheap, and the price is really reflected in the quality of their service. Most modern alarms can be hooked up to a landline and the alarm itself can call your cell phone, this will almost always get a hold of you faster then a monitoring center. The upside of a monitoring center is that they'll send a guard if you can't get a hold of them, but again they can be somewhat slow in doing that at times. If you have it call your cell phone, and you're worried that you might not be able to make it sometimes, then you can organize something with a local patrol company. They'll usually be happy to have you as a "response" client, where they will attend when asked (and you pay per callout) and will usually hold keys and such. They'll likely charge you a keyholding/account maintenance fee, most of them seem to be around $20USD/yr (although I imagine it'd be cheaper where you are).

CCTV:

First off a CCTV unit is only is good as how well it's been hidden, and secured into position; and they're useless if you don't have an alarm (because the burglar will have forever to wander around and find the DVR, which seems to be fairly common). What CCTV units are good for is for gathering evidence and assisting with ID'ing the person who broke in to your home. I haven't had the opportunity to mess about with the free/oss linux solution mentioned by the commenters so I can't comment on that. There are heaps of very cheap chinese no-brand CCTV units on the market that are very cheap. For a while I was tasked with testing heaps and heaps of different ones of these, trying to find something usable. Them crashing (and stopping recording) without notifying the user was fairly common. Another thing about them was a lot of them only offered the full feature set via a browser, which used ActiveX and usually only worked with IE6. With the brand name DVR's you're often limited to ActiveX (IE) browsers as well, but I found most worked past IE6 at least. It was only some of the vastly overpriced models ($2500USD+) that didn't require ActiveX, instead using Java. The brand name ones I tried didn't have any stability problems.