I was at Wally-Mart the other day and they had (and I bought) an inexpensive LASER bore sighting tool.
It's made by www.laserlyte.com. And it cost about $30/$40.
It's a long pen looking thing, with the LASER end much larger than the rest, the LASER end tapers smoothly into the long part.
And one the end of the long skinny part, you screw on a plastic "plug" for the caliber of your gun. Then insert the plug end, into your barrel and push it in and then give it a twist or two to tighten the plug.
And it really works well. It has several different "plugs" for different calibers. From .22 on up to .50.
I can't seem to find the exact one, but this is what it looks like (case is different etc... only the LASER device is the same)

But for the cost, it was really worth it. Drives the dog crazy, but worth it.