Ruger's 10/22 Carbine, chambered for .22 caliber Long Rifle.
I've been looking at purchasing a .22 rifle for a while, for a number of reasons.
They're cheap - this one was under $200, and you can find others for just under $100.
They're cheap to shoot - my favorite gun, the FN PS90, fires rounds that cost about $20 per box of 50. This gun fires rounds that cost $20 per box of 500. I can stay at the range all day shooting this gun without breaking the bank.
They're fun to modify - I like tinkering around with guns. It's the same thing I enjoy about computers. Some guns, like my PS90, are too freaking expensive to tear apart and mess with. This gun is the perfect candidate to tinker with. I already have plans to replace the stock, swap out the bolt release with an automatic one, and replace the factory iron sights.
My wife and I took this to the range today and put several hundred rounds downrange. It's just a fun gun to shoot. Maybe that's why most gun owners have one.