The AppleCare warranty for my 20" iMac is about to expire. Can anyone suggest a good 3rd party offering reasonable warranties that they've been satisfied with?
Has your mac had reliability issues?
If it has, you should consider buying something more reliable. If it hasn't, you don't need to waste money on something so useless as an extended warranty.
So you have already extended the warranty from one to three years with AppleCare but you still want to extend it even more? I doubt there are any companies willing to extend it even more for reasonable price as it's 3 years old so a mechanical failure wouldn't be abnormal.
I wouldn't pay more than $100ish/year anyway. If you are paranoid, just sell it and let the new owner worry about it and get a new one with AppleCare