OpenX this morning announced it has entered into a multi-year partnership with Microsoft that will allow the companies to “cross-market and promote products” to their respective publishers.

Under the agreement, Pasadena-based OpenX becomes a preferred partner to publishers for enterprise ad serving solutions and has agreed to promote Microsoft’s Content Ads monetization products and eventual future products to its own roster of web publisher customers.

We’ve talked about online ad server OpenX quite a bit in the past, and for good reason. The company, formerly known as Openads, is led by former AOL CEO Jonathan Miller (Chairman) and ex-Yahoo exec Tim Cadogan (CEO) and has in the past shown it’s serious about growing fast and making money in the process.

More recently, we covered the launch of OpenX Market, an alternative online ad exchange platform operated by the Pasadena, CA-based company.

Today, OpenX is announcing that it has raised a Series C venture capital round to the tune of $10 million, which brings the total of funding raised by the company to a healthy $30+ million.

OpenX, the largest neutral online ad server for website publishers, is finally ready to take the wraps off of OpenX Market, a service that has been in the pipeline for quite some time and was anticipated to make some waves in the digital advertising industry. I have my doubts about its disruptiveness, but website owners and publishers already using OpenX (we use it at TechCrunch) or planning to switch soon are sure going to want to take a closer look at the service, which is being launched in beta today.

In essence, OpenX Market is an independent marketplace where publishers can connect to advertisers directly to sell their ad inventory, while advertisers (either directly or via agencies) can access targeted inventory. Publishers define a minimum “floor” price for their ad impressions. OpenX Market then runs a real-time auction for each impression, with advertisers doing the bidding. If the winning bid from the auction is higher than the publisher-set minimum price, the higher paying ad is served and the publisher makes more money. If the winning bid is less, the publisher’s original ad runs.

OpenX (which used to be called Openads), provider of an open-source ad serving solution for web publishers – we use it at TechCrunch -, is growing like weed under the leadership of former AOL CEO Jonathan Miller, who is the company’s chairman, and ex-Yahoo executive Tim Cadogan who is CEO. According to the company, they’re serving well over 300 billion ad impressions through its software as of this month, while its Hosted product line has achieved a more than 1 billion monthly ad impression run rate.

In August 2008, OpenX announced the launch of version 2.6, an update to its downloadable ad server and introduced a couple of features which spurred usage of the system, including a new API, dashboard and a speedier ad tagging system.

Last March, Google began inviting a select number of publishers within its AdSense network to test a new hosted advertisement management tool called Google Ad Manager. The search company has now announced that the tool is out of beta and available to all publishers with AdSense accounts.