ditto on using Simple Green...I've found that it's the best degreaser...also, if you don't have a "grunge brush" (got one from a catalog a while ago and that's what it's called), which has different bristles at each end, then a toothbrush works fine too...I know some folks who regularly use a pipe cleaner for insertion in their chain links, but I never have. I have made it a practice to replace my chain about every 2000 miles as preventative maintenance, following a veteran cyclist's recommendation. So far, no breaks, no chain problems whatsoever, so I prefer to regularly make that small inve$tment to keep it that way!
fyi, I've never taken my chain off to clean...I just clean and lube it regularly...cleaning after the ride...checking it and applying lube before I ride again.