Some of the Lindt truffles are very good...I think Kohl's carries them around Christmas.

While in Mongolia, of all places, I got to try some former east-bloc chocolates imported from Poland and they were good (mostly of the filled type).

Peanut butter flavor M&Ms are a triumph of sorts of American ingenuity, and maybe they'll bring back the peanut butter/strawberry jelly ones of a few years back.

Cadbury seems to have the most straightforward of the milk-chocolate recipes, followed by Nestle and then Hershey (which has staked out a unique Hershey taste).

As with beers, I'm sure there's a small-batch craft maker somewhere that runs circles around the mass-marketeers, but too much research in this area is dangerous for me.