Treatobacco.net contains a wealth of information on tobacco-related issues, including descriptions of the negative health effects, available treatments to assist with cessation, policy issues, and much more.
The National Cancer Institute offers information on a toll-free quit line, live chat with advice about quitting smoking, and other general information about smoking.
Smokefree.gov will guide you to quit lines and other smoking cessation advice. Information on clinical trials for new smoking cessation interventions that may be available in your area.
The American Cancer Society has an excellent guide to smoking cessation. It also describes the steadily increasing health benefits the longer you stay quit.