Paid search spending in the United States is concentrated in the four categories of retail, financial services, media/entertainment and travel, according to a report released yesterday by JupiterResearch, a division of Jupitermedia Corp., New York. The four categories accounted for 79 percent of the $2.6 billion spent on paid search in 2004. The report, “Vertical Search: Early Marketers Will Reap Rewards of Low Pricing,” said this finding means the search industry will develop much the same way historical media markets before it have, with the broad-based search engines spawning a raft of vertical engines dedicated to specific categories.