At 20 minutes after quitting:

• Blood pressure decreases
• Pulse rate drops
• Body temperature of hands and feet increases.

At 8 hours:

• Carbon monoxide level in blood drops to normal
• Oxygen level in blood increases to normal

At 24 hours:

• Chance of a heart attack decreases

At 48 hours:

• nerve endings begin regrowth
• ability to smell and taste improves

Between 2 weeks and 3 months:

• Circulation improves
• Walking becomes easier
• Lung function increases

Between 1 to 9 months smoke-free:

Starting as early as a month after you quit smoking, and continuing for the next several months, you may notice significant improvements in these areas:

• coughing
• sinus congestion fatigue
• shortness of breath

At One Year Smoke-Free:

• Your excess risk of coronary heart disease is decreased to half that of a smoker after one year

At 5 years smoke-free:

• from 5 to 15 years after quitting tobacco, stroke risk is reduced to that of people who have never smoked.

At 10 years smoke-free:

• risk of lung cancer drops to as little as one-half that of continuing smokers
• risk of cancer of the mouth, throat, esophagus, bladder, kidney, and pancreas decreases
• risk of ulcers decreases

At 15 years smoke-free:

• risk of coronary heart disease is now similar to that of people who have never smoked

From:  http://quitsmoking.about.com/cs/afterquitting/a/after_quitting.htm