Wow, congrats & good luck to all those quitting. As a former two-pack-a-day smoker who first lit up at fourteen, I can certainly sympathize. I still haven't fully quit -- I buy a pack of smokes every time I get drunk -- but I don't smoke on a daily basis any more, which is a big step for me. And considering that I only get drunk once or twice a year these days, I figure if I never smoke outside of drinking binges, I'm not doing too bad, relatively speaking.
I quit without nicotine-replacement, because the hardest part for me was giving up the habit -- the sensation, the taste, the smell. I enjoyed smoking -- still do -- but it's not part of my routine any more, so I don't miss it as much. Identify the places and times of day you usually light up out of habit, and then make that situation undesireable for smoking. For instance, I used to smoke in my car. So I cleaned out the ashtray, removed the cigarette lighter, and had it detailed. Having that new-car smell back instead of the odor of stale tobacco smoke was a huge deterrent for lighting up.
Because so many people link cigarettes with alcohol, I reccomend staying away from bars, except smoke-free ones, until you've been off cigs for six months. When you eat out, order dessert or coffee -- it will help with with that after-dinner craving. And after sex...ice cream, man. Two spoons, one bowl. It's a beautiful thing.
I also used to smoke between classes at college with my friends -- that one I didn't give up until I graduated. If you have a group of regular smoke-break buddies at work, find something to subsitute for your smoke break. Visit this messageboard, call your SO, chug a coke. Your buddies might give you a hard time about not going out for a smoke with them, but be firm and resolute. Or, if you think you can handle it, go with them, but do something else with your hands and mouth -- drink a cup of coffee, eat a candy bar, yodel while doing card tricks. (Actually, carrying around a deck of cards to shuffle is kind of relaxing when you're full of nervous energy.)
I hope this is helpful. As arka said, "your mileage may vary," but if it's more about the habit than it is about the chemicals, some of the above may work for you. For the record, I didn't have a single cigarette between June 2000 and August 2001, and have smoked less than four packs worth since. From two packs a day to two packs a year is a victory in my book -- and that number is still decreasing, because I've discovered that now when I smoke more than three in a night I wake up with a headache that lasts three days. Someday I hope to reach the point where I can go drinking in a bar without feeling the need to smoke, but I'm not there yet. Good luck to all of you, and may you find success and satisfaction elsewhere in life.