Financial services marketers accounted for the single largest proportion of those ads, 28 percent; that figure is unchanged from February, but up from 22 percent in March 2005. Telecoms represented 17 percent of online ads, almost double last year's 9 percent, while retail goods and services accounted for 15 percent of online ads, up slightly from last year's 14 percent.

Spending for Web media--last year the no. 2 category, accounting for 18 percent of online ads--represented just 12 percent last month. Travel, which also was a big spender last year--generating 7 percent of impressions--last month accounted for just 3 percent of display ads.

E-mail sites garnered 42.6 percent of the ads--far more ads than any other types of Web properties. General community sites picked up 17.4 percent, and portals and search engines accounted for 9.2 percent.

The single most popular site was Yahoo Mail, drawing 30.3 percent of all online ad impressions--up fourfold from last year's 7.8 percent. MySpace came in second, with 15.6 percent--marking a fourfold increase from last year's 3.8 percent. MSN Hotmail garnered 10 percent of impressions, compared to 7.8 percent last year.

Nielsen//NetRatings' AdRelevance doesn't include in the data ads served on proprietary America Online pages, accessed only by AOL subscribers--but counts ads that appear on AOL pages accessed via the Web.

Online Display Impressions March 2005--March 2006

Source: Nielsen//NetRatings AdRelevance