Besides the addiction to nicotine, what else keeps me smoking?

The addiction to nicotine certainly makes it hard to quit, but so do some of the behavioral aspects of smoking. Smoking also provides other side benefits which are real. These are some of the other reasons it's hard to stop. See which of the following areas seem to be important to you, and then note some of the solutions to minimize their importance as you plan to quit. 

Stimulation. It helps you wake up, get organized, and get going. 
Plan ahead. Organize the day so you won't need a cigarette to get going. Go to bed early, plan some early exercise.
Chew on gum, brush your teeth to give your mouth some stimulation.
Avoid fatigue 

Handling. You enjoy some of the rituals of smoking. 

Doodle
Handle a coin or rock.
Clean or polish your fingernails
Wear a rubber band around your wrist and snap it. 

Pleasure. If you enjoy the "luxury" of the feeling that smoking gives you, then 

Keep a list of the pleasures of non-smoking.
Keep a list of the displeasures that smoking already or will cause.
Begin an enjoyable exercise program.
Treat yourself to something special. 

Relaxation. Smoking can be the classic "crutch" in times of discomfort. You may find it much easier to stop when things are going well, but particularly difficult when things are going poorly. 

Try to find other relaxing alternatives, such as listening to music, a walk or a talk.
Take up a hobby or sport.
Take deep breaths. Learn other relaxation techniques.. 

Craving. Join the club! That's the combination of the physical, mental, and psychological components of this complex and powerful addiction. 

Change your routine. Take a different route to work. Drink tea if you're a coffee drinker, etc.
You may benefit particularly from nicotine replacement therapies noted below. 

Habit. You smoke automatically. Chances are you don't enjoy many of them. 

Throw away your cigarettes, ashtrays, etc.
If your spouse or friends smoke, designate a part of your home as "smoke-free".
Go to places where smoking is prohibited, such as theaters, libraries, etc.
Always sit in the non-smoking parts of restaurants.
Have your car cleaned.