I seem to recall a longtime offender that generated a lot of complaints from DXers was 1110 WBCA in Bay Minette, Alabama. It and 1360 WMOB were both Buddy Tucker-owned stations that seems to "forget" to power down or power off on a regular basis. Both are currently off the air, though.
Right now for me the biggest offenders seem to be a few daytimer ethnic stations out of Atlanta. WPBS 1040, WFTD 1080… WQXI 790 is also now audible here most nights. It does throw a lobe my direction after dark, so I can't say it's 100% cheating but I almost never heard it post-sunset until it switched to carrying China Radio International.