looking for a good shotgun

If you've read my last post, you'll know that I'm now in the market for another shotgun - the one I spoke of is a Savage that dad bought for me over 30 years ago and it's been a great gun. I'm looking for a decent used shotgun for under $500 (this gun is coming out of my Hunting budget so I need to be kinda cheap).

In the opinion of my gunsmith, the Remington model 870 is the best shotgun ever built - If I can't get my hands on one, what are some other good makes and models? I'll be hunting primarily waterfowl and partridge with it, and forest grouse with my old shotgun.