Be sure you and your boss agree on your title and job description: You can't accurately assess the market value of your job if you think you're an advertising director and your boss thinks you're an assistant advertising director, although your title is officially "Deputy Idea Manager of Creative Media and Conspicuous Communications."
Salary.com says there's a good chance your employer has already assessed your "benchmark" position, so make sure you know the context for the company's salary decisions. It's also important to know which organizations your employer views as peers for pay comparison—these may be direct competitors, and they might be located nearby, according to Salary.com.
The Internet has lifted the veil on lots of previously private information—think of what Zillow.com did for home values—but the process of negotiating for a salary hasn't changed much. It's still in a company's best interests to try to hire or keep you for as little money as possible, and it's still in your best interests to ask for more with class, graciousness, and zeal.