if you can find them, mossberg makes a really nice extended modified tube that works great in the 500. I found one at a local gunshop, and i like it so much i sold the gun and kept the choke. Mossbergs are fairly common in my family so im sure it will get some use.
Carlson's chokes are awesome too. I run them in my 935 and really really like them. In the field they perform like nothing else with lightning steel loads. Going to do some patterning this summer and see if they look as good as they shoot.
The only thing about the mossberg 500 that i had, absolutely hated number two shot. I couldnt kill anything with it when shooting twos, but after switching to ones, it was one of my favorite guns to shoot.