Here we go again.

The Internet giants are falling back in love with finance. After several years during which the big Internet players were content to let Yahoo! ( YHOO) be the go-to site for stock market data, Google ( GOOG) and Amazon.com ( AMZN) this week showed they are interested in adding to their revenue by sticking their toes in the financial sector.

First, Amazon launched its financial services shop, announcing it signed up Fidelity Investments as the store's "featured partner" -- as Nordstrom ( JWN), Wine.com and Dean & Deluca are in other categories. For now, Fidelity is the site's only financial-services partner, and what little content is there, including a so-called blog, reads like ad copy for the fund family.

Amazon's move could signal either a disturbing trend -- the retailer rents out chunks of its respected domain as ad space for other companies -- or a welcome one: Opening up its generally affluent, educated and tech-smart customer base to a variety of financial services while allowing them to compare information on fees, funds and customer satisfaction.

Then, on Tuesday, Google took the wraps off of Google Finance, a site offering news and data primarily related to the stock market. Initial reviews of the site were mixed and cautious, if not critical. "Thumbs down for Google Finance," read the lead on Marketwatch.com. Self-appointed market pundit Henry Blodget, who made a lucrative career out of being wrong about the Internet, proclaimed "the beta landing page couldn't be less revolutionary."

As anyone with Internet access knows, Google has made some notable missteps of late, just in time for a public-image backlash. So, the safe move here would be to instinctively kick Google's entry into financial content. Don't trouble your brain, just let your knee-jerk do the thinking for you.

The big criticism seems to be that Google's new site isn't very new. To say that Google Finance looks an awful like the entries in this race -- Yahoo! and Microsoft ( MSFT) in particular, as well as dozens of smaller sites, including TheStreet.com -- is to miss what is truly ingenious about it.

At first glance, Google Finance does look like Yahoo! Finance, which, according to NetRatings, has 12 million visitors a month, and MSN Money. The similarities to these sites is welcome, since it gives Google Finance a familiar and user-friendly feel. But dig in and there are some subtle but significant differences.

Stock charts can be dragged, Google Maps-style, to reveal older price patterns. Scrolling over the chart reveals price and volume, a feature that is going to thrill technical analysts. If you don't know a company's ticker, you can just type in the name -- a needed feature long lacking on Yahoo! Finance. The default page for an individual stock is at once the cleanest and most informative of any financial site out there. It even links to pages showing a company's open jobs, which some investors like to track because it signals expansion plans. And unlike Yahoo!, Google Finance will yield results for private companies.

This site is a shot across Yahoo!'s bow. Yahoo! Finance has long been a big part of my workday. But it only took me about five minutes of poking around Google Finance to realize I will probably be spending more time with it than with Yahoo! I'm not alone in making that shift: Yahoo! is going to have to spend a lot of money improving its own finance offerings. And that competition will help users, just as the Yahoo!-Google search race improved search engines.

For Google, the move into finance-related matters is a little trickier than it is for Amazon. On the one hand, investors are getting antsy for Google to produce new revenue streams because the search business is going to slow down as it gets bigger. And while Google Finance has no ads on it yet, it could easily open the door to new ad revenue and marketing partnerships.

On the other hand, as blogger John Battelle notes, nobody has been eager for Google to get into the moderating of content -- having to remove user comments that violate its rules, for example, vs. simply organizing pages from other sites in its own search results. Message board flare-ups have caused Yahoo! more than its share of headaches.

Moving away from the passive organizing of content makes life a little more complicated for Google and could open up a few cans of worms. But something had to give -- the need for new revenue won out, as it would at most companies -- and Google is growing into new business models, worms be damned.

That Google and Amazon are branching into financial-related services and content may not be a coincidence. The tech-stock crash is far behind us, and even some of the more cautious investors are starting to dabble in technology stocks again. It's almost as if the bad memories of the early part of this decade are being erased.

And in a way, they are. Look at Google's chart of the Nasdaq and click on the option to give the "maximum" view. It only stretches back five years, to March 2001, when the index was trading just below 2,000. It's almost as if the great tech bubble never happened.