American Heart Association
The American Heart Association (AHA) identifies smoking as one of the "six major independent risk factors for coronary heart disease." Smokers are more prone to blood clots and less likely to be physically active, both of which affect heart health. Their "quit smoking" page combines detailed information on smoking's health risks, along with resources to help you quit, fight the urge to smoke and create a plan to quit and stay that way.
Their quitters plan is a little bit less involved than some of the other services out there. Rather than an interactive site, the AHA provides ideas for dealing with the urge to smoke, whether you're home, outside or in social situations. They encourage smokers to "keep a list of pleasurable activities you can do when you feel urges during your transition phase."