I got a breech plug stuck in a rifle today. Any suggestions how I might get it out?

Kroil works.

I got this from sabotloader, take the barrel out of the stock get a pan of boiling water and soak the breech end in the boiling water, then take it out and the plug should come right out.

If you can remove the barrel, as sqezer said... Works. Or heat the area with a torch as a last resort, I have poured boiling water down a barrel, heating it. Wear gloves, then secure the barrel in a vice.

Please make sure its a padded vice or wrap a towel or something around the barrel.
You can also spray Liquid Wrench down the bore and on the breech itself. But I would try soaking in hot soapy water first and then get a socket on it and once you get it moving don't try to take it all out at once. Work it back and forth to get the grit out of the threads.
And next time put more antisieze on those threads.

I'm not big into in-lines but I put BEL-RAY brand molylube anti-sieze on anything that has a possibility of getting stuck (like the breechplug of my Firestorm flinter) and have never had a problem removing anything I've used it on. The manufacturer states that it is a stable, non-melting, multi-purpose lubricant that can prevent seizing and galling of pressures over 100,000 lbs. per square inch.

BPS

A few years ago when I bought an abused Remington 700ML its breech plug was BADLY frozen. After a two day soak with Liquid Wrench it came right out.

Thank you everyone! I got it out by soaking in boiling water. It was a heck of a job that I would wish on no one.