If you truly don't want to risk killing the intruder, get a taser or some other less-than-lethal method of defending yourself may be the way to go.
However, if you don't mind killing if absolutely necessary, here's my advice.
Being shot by a .22 will not necessarily scare off an intruder. Brandishing a firearm, firing a warning shot, and even shooting an intruder will sometimes deter them, sometimes it won't. Every month American Rifleman lists a bunch of newspaper articles about citizens excercising their constitutional rights to defend themselves, and I'd say more than half of them mention that the intruder doesn't leave simply because of the threat of a handgun.
Something like a .32, .38, .357, or 9mm will probably work as a more effective means of causing your intruder to flee if shot, so long as you don't get hollow points or any kind of Magnum or +P rounds. None of these rounds, in basic form, are reknowned for their ability to drop a target, but rather usually take a few shots to drop your target. Obviously if you shoot your intruder in the chest you will probably stop them, but if you go for a wounding shot these will probably work to cause your intruder to flee.
After that, you have the man-stoppers. .357 Magnum with hollow points and .45 ACP (you can get hollow points, but this doesn't need them) are pretty standard, and can be fired from reasonably sized platforms. The calibers I listed as wounders do an okay job with hollow points as well. .40S&W works ok too. I'd recommend a minimum of the .357 Magnum with jacketed hollow points, but I highly recommend getting something chambered in .45 ACP, as this will leave a bigger entry wound with standard ammunition. It can really do some damage if you bump up to hollow points or +P ammunition. These are true man-stoppers.
After that, you have the "most powerful handgun in the world" contenders. The only drawback to these is that they are heavy and quite large framed (and the majority are in revolvers, if you find that a disadvantage). This would include your .50 AE, .44 Magnum, .500S&W, .454 Cassull, and others. These WILL stop your intruder, even if that intruder is a water buffalo (for the .500S&W that is). These don't sound like what you are interested in, but these will exude a high "scare factor" that other handguns won't, simply because of their size.
One other piece of advice I can offer is to consider a shotgun. A 12 gauge, at close range, is going to defitely stop the intruder. Any shotgun at close range will, as a matter of fact, but if you bump down to say a .410 with bird shot, you could probably fire across a room and stop your target without killing him.
Now, to respond to the "guns are evil and will kill you in your sleep" crowd. I'd like to see these statistics about a suirt gun being better, and how if you own a gun it WILL be used against you. The way an attacker usually takes a firearm from the user is either a) the attacker breaks into your home at night and finds your firearm (in which case they could just as easily get a knife from your kitchen and kill you) or b) the user draws the firearm without the willingness to kill.
You need to think long and hard before owning a firearm, especially one used in self-defense. You can always attempt to scare off your intruder, or hold them at gunpoint until the police arrive, but that is not going to work 100% of the time. If you know you won't be able to not just fire, but to kill, a firearm is not for you. I suppose you could just not buy ammunition and rely on the scare tactic, but then what do you do if it doesn't work? At that point, I think you are better set with a less-than-lethal deterrant, like a taser. Check out Kimber's LifeAct products for that.
However, as Grizzly has stated below me, you should probably get serious about personal defense, and realize that we unfortunately don't live in a nice fuzzy world where the bad guys always lose to the good guys.