Even bellwethers know when to swallow their pride and flash a little flexibility. Just ask Yahoo! (NASDAQ:YHOO) and eBay (NASDAQ:EBAY), who have announced a strategic alliance that will showcase their respective core strengths on both sites.

First, we have Yahoo! serving up graphical ads on eBay. That's important news, because if eBay were to ever implement the more lucrative targeted text-ad blocks that Yahoo! and Google (NASDAQ:GOOG) have popularized in recent years, power sellers would be hopping mad. It would be difficult for eBay to justify its premium listings if the individual auction pages were wallpapered with contextual ads for competing products. Instead, text ads from Yahoo! will show up on search result pages for complementary products, and even that will be a delicate issue if it is implemented too ambitiously.

That's about the only area where eBay and Yahoo! are showing some restraint, because the deal is pretty aggressive just about everywhere else. For starters, eBay's popular PayPal service will now be the electronic payment option of choice with Yahoo!'s online wallet. That makes sense, since Yahoo! axed its similar PayDirect service nearly two years ago.

One of the more tantalizing aspects of the deal involves eBay's Skype. Sites like Google and Miva (NASDAQ:MIVA) have been offering "pay per call" ads, through which sponsors pay for voice leads to a unique telephone number. Yahoo! will now be able to explore the possibility of piggybacking on Skype's success in Web-based calls to promote a "click to call" service through Skype or Yahoo! Messenger.

This may be as deep as this relationship gets, though I'm guessing that it's just the beginning. Both companies have been portrayed as laggards lately, given Google's faster growth, and it's not really a fair knock given eBay's great acquisitions and Yahoo!'s global expansion efforts. Now they have a chance to analyze each company's offerings and drum up a "best of breed" solution that, if successful, will make Google matter a little less.

If not? An angry Google can be a fierce competitor.

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Longtime Fool contributor Rick Munarriz is a satisfied eBay user, nd he's got the 166 positive feedback points to show for it. He does not own shares in any of the companies mentioned in this story. Rick is a member of the Rule Breakers analytical team, seeking out the next great growth stock early in its defiance.