There are few things that Google (NASDAQ:GOOG) loves more than ads and mobs, so it wasn't surprising to see the world's leading search engine snap up mobile marketing network AdMob this week in a $750 million all-stock deal.

I closed my coverage of the deal with two meaty questions:

  • Is Google conserving its greenbacks for an even bigger purchase?
  • Does Google feel that its stock is expensive at this point, making it ideal legal tender?

The latter was answered almost immediately, after CEO Eric Schmidt revealed that the company will embark on a $750 million share repurchase -- the first in Google's history, apparently -- to offset the deal's dilution.

In other words, this wasn't Google making a valuation call. Either AdMob demanded stock as currency, or Google feels that the acquired company will be more productive if it's tied to its stock's performance.

Now let's tackle the first question. Even if Google is, in theory, turning a stock deal into a cash one via the repurchase, this is still a company that began the quarter with a whopping $22 billion in cash and short-term investments on its balance sheet. The interest being generated on idle cash is pathetic these days, so it's not surprising to see so many cash-rich companies in buyout mode.

If Google keeps shopping -- as it very well should, since acquisitive fever may lead a rival to snap up one of Google's coveted targets -- what should it buy? I have a few ideas.

Facebook
With 300 million users -- tacking on new Facebookers at a breakneck pace of 50 million every couple of months -- the world's largest social-networking site is a hub to 5% of the planet, and a much larger percentage chunk of the Internet audience.

This isn't just about the sheer volume of page views. Google doesn't play that game, and rightfully so. Yahoo! (NASDAQ:YHOO) actually serves up more pages than Big G, but it commands just an eighth of the market cap. Carving out a lucrative online life is more about the quality of traffic than the quantity.

I believe that Facebook excels on both fronts, despite social networks' bad rap in general. Facebook users publicly post their interests and whereabouts. They bond with like-minded friends. Google would have a field day serving up contextually relevant ads, beefing up its local search business in a major way.

Ancestry.com (NASDAQ:ACOM)
The leading genealogy site went public this month, so Google has a shot to grab it while it's still in the crib.

Ancestry.com is profitable and growing quickly. Website users have created more than 12 million family trees, lush with profiles of 1.25 billion descendants. This isn't a perfect model; the premium subscription approach brings in money, but it also attracts problematic churn rates. It's also just a matter of time before free, ad-supported models make a bigger splash.

However, Google's prime business is attracting folks looking for something. Isn't this what Ancestry.com is all about?

IAC (NASDAQ:IACI)
Is IAC's Ask.com on the block? CEO Barry Diller hinted at the possibility when he called the search business "challenging" during last month's quarterly conference call. Most analysts agree that Microsoft (NASDAQ:MSFT) is the most logical buyer if Ask.com is indeed for sale. Google can't let that happen.

Microsoft is gaining momentum with the surprising popularity of Bing and its paid search deal with Yahoo!. Ask.com would be a smaller piece of that puzzle, but clearly an incremental one.

Google can try to outbid Microsoft for Ask.com, but it may be better off trying to swallow IAC whole. Now that Diller has completed the conglomerate's split, IAC consists of new media properties that would look great on Google's arm. From ServiceMagic for contractor referrals to local-hotspot hubs Citysearch and Urban Spoon to slick video-sharing site Vimeo, IAC has dozens of prolific properties worth monetizing the Google way.

The Knot (NASDAQ:KNOT)
I've been promoting The Knot as a potential buyout site for years, to no avail.

I don't understand. The Knot would be perfect for any search engine. As the country's leading wedding-planning site, it attracts millions of brides and grooms eager to make their nuptials as special as possible. The online leads and referrals business doesn't get any better than that.

The Knot has struggled financially during the recession, but that's temporary. Folks who have delayed their weddings or scaled back plans will eventually come around, giving Google a great "buy low" opportunity.

Twitter
Fellow Fool Tim Beyers and I pitted Facebook against Twitter six months ago. I still think Facebook offers a richer, stickier experience than Twitter's one-trick pony, but Google already has a working relationship with Twitter's founders, and it's a logical fit.

Search engines need to stay relevant as portals. If they don't stay current, they'll wake up one day to see Time Warner's (NYSE:TWX) AOL in the mirror. Folks who have Google or Yahoo! as their home pages are probably switching over to Facebook and Twitter these days. News breaks on Twitter. The online world's real-time pulse is measurable on Twitter. It's the ultimate customized experience.

Even if Google doesn't want to pay up for Twitter, it can't afford to let Yahoo! or Microsoft beat it to the offer.

So get cracking, Google! $22 billion can go a long way, but it's going nowhere on your balance sheet.  

I've summed up my selections in the poll below. If you've got ideas of your own, feel free to share them in the comments box.