Depends on the species of cat. For channel cats I normally use some sort of prepared punch bait with a slip-sinker + #6 treble hook rig. I've had good luck with both "Shad" and "Monster" flavors from CJ's Bait Co. I've got some Team Catfish "Sudden Impact" punch bait on order right now to test out, several sources online say that the Team Catfish bait stays on the hook better and will attract more fish. We'll see, I caught 5 channel cats yesterday in a little over an hour before a storm rolled in using CJ's bait. I've used chicken livers, chicken hearts, cut bait, hot dogs, etc for channel cats and have always had the best luck with prepared baits (punch or dip). I prefer punch baits over dip baits as the dip bait seems to require reapplication more often than a good punch bait.
For blue cats, live/cut shad or some other form of fresh cut bait on a slip sinker + circle hook rig works for me, the action is much slower than channel cat fishing though.
I haven't specifically targeted flathead catfish before but the general consensus is that live bait (shad, goldfish, etc) is the way to go for them.
