I have been using an RWS 36 in .22 cal.  It is a break-barrel gun, so you only have to do it once.  It is a lot quieter than a CO2 or compressed air gun, so it doesn't wake up the woods when you shoot.  I have shot woodchucks and had a couple of 1-shot kills within 25 yds.  If you go this route, make sure to get a scope that is rated for the spring-air guns or you will wreck them in no time.  Also make sure to get airgun rings with the scope-stop pin or else it will move on you.