Doughball is the bait of choice for me, but that's because I fish deep water and am not "sight fishing". Bread won't sink as bad as doughball and will allow you to stay in the strikezone longer. Here's how you should rig your line for sight-fishing Carp.
You need a baitholder-style hook, the kind that has little barbs on the "neck" of the hook to help brittle baits stay on longer. Eagle Claw makes them and you can buy them at Wal-Mart. Look for the size "#4", these will be a good all-purpose Carp hook. May want to buy a few packs of #6 and #2's as well.
You need some teeny and I mean TEENY split-shots. The smallest removable split-shots that you can find. You'll need to add one of these about 12" from your hook/bread. This will allow your bread to sink a little and let you cast farther than with just bread and a hook.
Have a steady supply of bread, corn, and nightcrawlers. Try corn, bread, and nightcrawlers rigged on the hooks with a split shot above it. The #2 hooks are best with nightcrawlers, the #4 hooks are best with bread, and the #6 hooks are best with corn.
Make sure your reel has a smooth drag and keep it relatively loose. Play the fish well. If you learn to play a fish well enough, you'll be able to easily catch those 15lb plus Carp on 6lb line.