I've recently done a lot of research on air rifles and air pistols. I got a crosman custom shop 2300KT, (2240):
http://crosman.com/custom_store/1/step1
It is spooky accurate with a little red dot on it, (for a pistol at 40-75 feet), with Jumbo .22 pellets. It is very loud, (even with a 10" barrel). It shoots at about 580 FPS after I made some modifications to it, (custom valve). It's CO2 and I get about 20 shots per CO2. I've got about $200 in the pistol. It will take a tree rat down with a decent body shot although I always go for the head. It's got the 10" barrel, cheap target grips, a long-steel breach with a very long run of groove on the breech to mount lots of different optics.
I have 3 prime producing pecan trees in our yard. The city I live in was literally built on one of the largest Pecan Plantations in the United States during the late 1800's. We got lots of tree critters and they are fat and juicy.
About 12 years ago I took over 40 out of our yard alone in about 2 weeks after a population explosion caused by one of the best Pecan harvests in 35 years of record keeping 3 years prior to that. I BBQ'd them, smoked some, fried some, and made Gumbo with some as well. I was using an ancient, rebuilt Benjamin Pump 22 ... with an ... uhhhh ... adapter.
For a QUIET, POWERFUL air rifle that will shoot a 22 pellet fast and hard, a new type of springer air rifle, (nitro piston), is being produced and sold by crosman at a very good price.
It's an "air piston" springer, not a physical metal spring. And the air piston is filled with NITROGEN which is unaffected by cold or heat to a great degree. The air piston inside is very much like the air pistons used as shock absorbers on car trunk lids, (hatchbacks). You can leave these things cocked and loaded for as much as a week and only loose a few percent of the pressure, (you can't do this with springers as it will ruin the spring and stress the seals, etc.. ). They really are an interesting air rifle.
It's here:
http://www.pyramydair.com/s/m/Benjamin_Trail_NP_XL/2052
It's a bit pricey at $299, and it will shoot about 900FPS, (realistically), with heavy, Jumbo, 22 pellets. It's been reviewed in depth by "B.B. Peltier", and the bugs have been worked out in production. It's an awesome air rifle. It was introduced at the Shot Show early this year.
It's got a little cousin at $229.00 :
http://www.pyramydair.com/s/m/Benjamin_Trail_NP_Nitro_Piston_Hardwood_air_rifle/2050
It will only shoot about 750 to 850 feet per second depending on the weight of the pellet you are using. It's a bit smaller as well. It only comes in 22.
I'm going to get one of these one day when I finish buying about 20 or 30 more BP arms ... of course.
Oh, by the way, you CANNOT use black powder in these guns.