Working in online ads for the last decade or so, I've seen lots of market segments start to take advantage of online advertising --

-- sometimes proactively, more often as a competitive reaction. What's always fascinated me most, though, were the categories that hadn't yet "popped."

Sometimes this tardiness stems from the market itself not being fully ready (auto sales in 1998 or local real estate in 2006). But more often than not, it stems from simple marketing department inertia. Where there is irrational inertia, there are market opportunities for those cleverer and fleeter than the old school.

Back during the bust, I often thought it would be fun to buy a distressed firm in one of these fields to turn it around with some run-of-the-mill rational marketing. The inspiration came from experience at ad agencies, where it slowly dawned on me that my clients' success often had more to do with our competitors' incompetence than anything we were trying to do.

Here is my list of the top few markets where shifting budgets to online media would make enough of a difference to allow a firm to vastly increase marketshare:

1. Real Estate. There are plenty of real estate sites out there, most of them garbage sites designed to suck in traffic to make money via providing low-quality inventory to search engines. That impression of the market state -- which is currently a fair impression -- hides opportunities.

Local realtors have to get their location-specific listings out to folks looking intently within their market geography. The brunt of them simply submit their listings to a multiple listings aggregator and call it quits.

Online ads in local publications are a must-do. Search ads with the geographic terms are also a no-brainer, as a local realtor has the ability to make a much, much higher margin on keywords than one of those icky national search term arbitrage operators. In other words, the local realtor can profitably bid much higher for the search term "Podunk, Vermont" than can one of those content-free real estate sites. The average click from one of those ads might be worth $10, whereas the real estate portal can only make a few cents off each.

2. Local Services. They're getting better, but the local directories on Yahoo, Google and the like leave much to be desired. They're about as good on a good day as the local yellow pages and much worst for the rest. Looking for a plumber? A guy to pour a cement slab to hold a new oil tank in your basement? A fellow to prune your apple trees? The internet should be the obvious place to find these folks, but it's rather hit and miss.

Those individuals should, of course, have small sites that the search engines will index and send them free organic traffic. But the larger groups, the trade organizations, trade publications and others have an enormous opporunity to become directories for these various service providers. The culture of trade groups, cooperatives and trade publications is, well, not very updated, let's say, and I think this is the hurdle that has kept them out of their natural online habitat.

3. Professional Services. Psychologists, specialty lawyers, independent engineers, and similar professionals, should be actively advertising online. These practices typically survive on local word-of-mouth marketing, which is a wonderful thing, but it leaves a lot on the table.

Good professionals who are well enough established can go an entire career simply having folks come to them, but they often don't realize that they are missing out on lucrative opportunities. Local markets tend to drive price points that only the locals are capable of supporting, and communicating beyond that market can make a business bloom.

Just two days ago an architect who lives in a posh area of Vermont told me he had gotten a call a couple weeks ago from someone in LA who was looking to build a summer home. This southern Californian -- a species related to lemmings, capable of throwing their life's savings over cliffs and into housing bubbles -- asked that the structure "not cost more than $500 per square foot." For those not recently involved in a building project, that's sort of like going to a media rep and asking if he had any media under $500 CPM.

Point is -- distended, inefficient and unbalanced markets get corrected only as they flow out to to other markets, alternative suppliers and alternative products. These professionals can be an outlet for that market demand, if they're promoted online.

One fly in this fluid internet market utopia is that many states regulate just these professionals in a fashion that proves to be rather protectionist. Lawyers, engineers and the like often have to go through hoops to legally provide services in another state -- hoops that were instituted under the guise of consumer protection, but have much more to do with local trade guild protection.

Some other categories waiting to be opened up by the intrepid first-movers:

* Municipal services and equipment providers
* Tertiary defense contractors
* Industrial fittings, fabrication and parts suppliers

In each of these categories, market demand is already present. Yet culture and inertia --- and sometimes channel conflicts -- prevent forays into online marketing. Those that find their way around those obstacles will win a substantially disproportionate share of a market that will likely be larger than their current one.