Paul Allen points me to an emerging sector that I hadn't really noticed before - web analytics:

"The largest company in this space may be NetIQ, which acquired WebTrends in 2001. NetIQ had revenue of $68 million in the quarter ended June 30, 2004 and a narrowing loss of about $7 million, but it offers many more services than just web analytics. It's hard to tell how much of its revenue comes from WebTrends. The company had more than 1,200 employees in mid 2002.

Every serious internet business must use powerful web analytics services. Web developers and marketers rely on these tools to determine how many visitors your site has, where they are coming from, the ROI of marketing campaigns, what products are selling, what paths customers take before purchasing, and how site design changes impact revenue. There are free and cheap web stats packages everywhere, but once you've used a high-end package, you realize they are the key to eliminating guess work from your marketing and design decisions..."