The two main hammers available are Volquartsen and Power Custom. Power custom is $5 cheaper and just as good. Both are easy to pop-in and will drop you down to around 2 1/2 pounds from 8 or 9 pounds of pull.
If you need installation help, I have a pictorial with nice photos and easy instructions on how to do any install to a 10/22 at
http://ruger22.comAlso, hammers are available at discount prices at
http://cheapgunparts.com Why are they cheaper? Simple. Most hammers come with a new hammer spring, but just about anybody who has shot a 10/22 will tell you the factory original hammer spring is much better than the ones in the aftermarket kits, so I work a deal to buy ONLY the hammers and pass on the savings.
Also, there is a review showing how the VQ and PC hammers stack up on the ruger22.com site.