Editor's note: This article has been updated. We mistakenly used PayPal's 2003 revenue figure of $438 million for its 2005 sales number. The correct number for PayPal's 2005 sales figure is $1028 million. We apologize for this mistake.

One of the most widely used arguments against Google (NASDAQ:GOOG) is that its revenues are generated from one source: online advertising.

Since those revenues happened to exceed $6 billion in 2005, it's not a bad problem to have when you are just 7 years old. It is a valid concern, though, when we consider that an extensive amount of future growth is currently priced into the stock. Any new products or services will face a steep climb before becoming a significant part of sales. As it stands now, I see three molehills that could, given some time, grow into revenue mountains.

One area for potential is non-Internet-based advertising, encompassing television, radio, and print. I've previously discussed Google's quest to take over the world advertising market. Capturing a part of that market could continue to fuel a high growth rate even if the Internet-based advertising market matures quickly. After the company's analyst meeting on Friday, Merrill Lynch analyst Lauren Rich Fine commented that capturing one-sixth of the $600 billion advertising market is a lofty goal. My conclusion is that just a few percentage points of that market in five years may be enough to make Google a worthwhile investment.

If you think non-Internet-based advertising revenue isn't a true diversification, then the move to monetize search in the wireless domain may be. Google believes that mobile devices may become the primary means of accessing data over PCs; it is the trend being seen in emerging markets. The demand for Google's mobile search services are most likely increasing, considering the recent deals to add those services in SonyEricsson, Motorola (NYSE:MOT), and Vodafone (NYSE:VOD) products. While the increased use of mobile devices is quite evident, it's not so clear just how and when the monetization of paid search is going to happen, or how lucrative it will be.

The final molehill is Google Payments, through which users can pay for items on Google Base or for using the Google Video and Google Earth services. Considering that Google Payments has often been considered a possible competitor to eBay's (NASDAQ:EBAY) PayPal, we can use it as a comparison. In 2005, PayPal generated $1028 million, or 22.6% of eBay's revenues. While I don't expect Google Payments to become 20% of Google's sales in the foreseeable future, generating $400 million-$500 million is certainly possible, considering how many people could end up using the service. That would represent 10% of Google's 2005 revenues.

While finding solid numbers to work with has been a rather difficult task when predicting the company's future performance, at least we are seeing the shroud of mystery being raised a bit. We have finally been allowed to get tiny peek at what direction management seems to be moving. It's still hard to determine what products will contribute significant new revenues -- should they ever appear. But while the Internet advertising business is still hot, management can be patient in planning the timing of new-product releases.

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Fool contributor John Bluis is patiently waiting for a better price for Google. He has no financial interest in any company mentioned in this article. The Motley Fool has a disclosure policy.