I found Robert "Sunlight" Gardner/Osmond particularly cruel.
Other then that: The Big Coffin Hunters, Rhea of the Coös, Morgan Sloat, Leland Gaunt, André Linoge, Mrs. Carmody, Collie Entragian. The list goes on, there are a lot of good villains in the King universe.
Ahem, check the name... Yeah him and plenty of others. Stephen King does villains very, very well.
Trying to think of ones that may have not been mentioned much yet. Ace Merrill (The jerk we love to hate), Carrie White's mother (hated her soooo much), I despised Jim Rennie with a passion too. Although he is more of a bit character, Brian Lippy in "From a Buick 8" made me giggle like a little kid (ED-E JACK U BOYS!!!) I also cracked up when Curtis Wilcox slammed on the brakes and made Brian fly forward and smash his face on cage in the police cruiser to shut him up. I could probably come up with 20 of my favorite Stephen King villains easily. Those are just a few off the top of my head that aren't too obvious.