Comparing Your Stats to the Averages
A clickthrough ratio of 0.5% may seem low, until you compare it to the industry average, which nowadays is estimated to be around 0.4%. It's also interesting to compare this to the average response rate for direct (snail) mail, which is 1.0% - 1.5% (Source: http://www.emarketer.com ). Comparing your click rates to those of other advertisers on the sites that you use, or to those of other clients of your ad agency, may be even more useful. Take average clickthrough figures provided by individual sites with plenty of salt, however, as they have an incentive to inflate them.
Obviously, comparing costs among different sites is always a good idea. Several factors influence how much a site can charge for ads, however, so you can't compare CPM figures directly. CPMs range from zero through pennies and dollars, all the way up to $100 or more. Sites with low traffic or less-than-premium content generally have single-figure CPMs. Sites that target hot ad markets, for example tech sites such as this one, tend to have CPMs in the $10 - $80 range. Search engines and portals have traditionally had the highest CPMs, partly because they are able to deliver very highly targeted groups of users. The tighter the targeting, the higher the price. Laser-beam campaigns, such as those that let you pick individual search words, can command CPMs well over $100.
Good ad agencies are very familiar with the average CPMs for particular types of sites and types of campaigns. In fact, they may very well pressure sites not to try to ask for a higher price than the average for their class.
Compare the costs of different campaigns with things like targeting and conversion rates firmly in mind. In a perfectly efficient market, you'd always get just what you paid for, and higher quality clickthroughs would be perfectly proportional to higher CPMs (and articles like this one would be unnecessary). But efficient markets exist mainly in the imagination of economists, and certainly nowhere in the advertising world. So calculate your cost per click for every campaign, and you should get a general idea of whether better targeting and other premium ad features are worth the higher prices.
Where to find all these stats? A good ad agency will be able to provide you with most of what you need to know. A really good one will provide you with a report that lets you compare all your campaigns with each other, and with pertinent industry stats, on a daily basis. The list of further resources at the end of this article should lead you to all the stats you can stomach. Do keep in mind that a lot of figures you'll see are based on estimates, especially the market research stuff, and can vary widely from one source to another.
Online Advertising Articles
Here you'll find various rants both for and against banner ads, as well as a lot of practical tips for ad sellers and buyers.
Cyberatlas
The source for Internet statistics, market research, demographics and surveys.
Internet Advertising Report
In-depth information and analysis of the Web advertising and marketing industry.
internetstats.com
Another source of general Internet statistics.
Internet Advertising Bureau
Lots of good info about online ads, including stats.
Adbility
Formerly MarkWelch.com, this excellent site features a list of almost every ad agency, network, and other online advertising-related firm out there, with honest feedback from users thereof.
Advertising Age
Advertising Age is a respected magazine about advertising, and includes a lot of helpful stats and other information.