before after Forbes.com CEO Resigns. Plans to start his own media company.After nearly nine years as the dominant force behind Forbes.com, CEO Jim Spanfeller is calling it quits.

In a memo circulated to staff this morning, Steve Forbes, president and CEO of Forbes, praises Spanfeller for his “monumental job” of building the company’s online presence to an audience of 18 million monthly users.

The story was first reported yesterday by AOL’s DailyFinance with a memo (shared below) now being circulated around the web after being posted by All ThingsD.

In the memo, Spanfeller explains that he plans to open his own cmedia company:

“The world of media has changed rapidly in the past 10 years and the velocity of the change promises only to increase going forward…I’ve had a great run at Forbes and have been deeply involved in the breakthroughs and transformations between traditional and digital media. Now I see a huge opportunity to have my own media management business that will help other traditional media companies make the most of their enormous prospects in digital venues, taking all I have learned here in the past decade and applying on a wider horizon. Forbes.com has truly been a truly wonderful ride and I am deeply in debt to the Forbes family for letting me be a part of it.”

Steve Forbes announced that Spanfeller would stay on at the company through Labor Day to help in the transition to a yet to be announced successor.

This is the internal memo:

To: All Hands

From Steve Forbes

July 16, 2009

Jim Spanfeller, President and CEO of Forbes.com has decided to step down from leading our website after nine years. In the entrepreneurial spirit that Forbes has always championed, Jim will be setting up his own media management company.

Describing his future plans Jim said, “The world of media has changed rapidly in the past 10 years and the velocity of the change promises only to increase going forward. I’ve had a great run at Forbes and have been deeply involved in the breakthroughs and transformations between traditional and digital media. Now I see a huge opportunity to have my own media management business that will help other traditional media companies make the most of their enormous prospects in digital venues, taking all I have learned here in the past decade and applying on a wider horizon. Forbes.com has truly been a truly wonderful ride and I am deeply in debt to the Forbes family for letting me be a part of it.”

Jim has done a monumental job of bringing Forbes.com to the lead position in business websites, and secured Forbes.com as the must visit site for not only global business leaders but also anyone interested in the finest business reporting and analysis available. At present Forbes.com has 18 million unique visitors a month.

Along the way, Jim has overseen the development and growth of Forbes Digital, which includes Forbes.com, ForbesTraveler.com, Investopedia.com, RealClearPolitics.com, RealClearMarkets.com, Real Clear Sports, and Forbes Business and Finance Blog Network, which together reach 40 million unique visitors a month.

This immense growth on the digital side of the business was spearheaded, pursed, and led by Jim with enormous success. The digital world is still uncharted with few rules, and Jim’s intellect, creativity, and business acumen helped bring us our number one position. For this the Forbes family is very grateful and we wish him all the success in his future plans.

Since Elevation Partners partnered with Forbes three years ago, Jim has worked very closely with them on the growth and development and vision for Forbes.com. Commenting on Jim’s departure, Roger McNamee of Elevation said, “Jim did a fantastic job leading Forbes.com. In an era when competitors feared it, Jim embraced and evangelized the internet, with huge benefits to Forbes and its audiences. We are grateful for his contributions over the past nine years.”

Jim will be staying through a transition period at least through Labor Day. Please join me and my brothers in wishing Jim all the best in the future, which he deserves.