Ruger Mark II. A family member has one and at 25 yards it was very accurate. I don't know if he got quite as good of groups as my Ruger 10/22 but at 25 yards they weren't far off. We both were shooting free handed btw. It's got quite a long barrel but is very accurate at least at 25 yards. Walther P22 is another popular one but I'm not sure how accurate it would be as it has a short barrel. May be accurate though I'm just not sure.
I've got a Ruger MK-II as well...Mine is stainless with the 6 7/8 target barrel...I use it quite a bit for squirrel hunting (when I'm not using my .40 flintlock)...It's good for head shots out to 25-30 yards...
I have a Ruger Mark II Target (5.5"), a Ruger Mark I, a couple Browning Buckmarks, and I just bought a Walther P22 (3.5") yesterday.
I had no problem shooting a few cottontails this evening with the new P22, farthest one I head shot was about 35 yards tonight. My only complaint is the sights are a lil too large for the small P22, makes it a little tough to get used to with such a short sight radius compared to my other handguns.