Sports statistics. NFL, MLB, NBA, etc.
I think the leagues fight hard to disallow this although they have recently lost a couple high profile lawsuits.
http://arstechnica.com/tech-policy/news/2007/06/mlb-tries-to...
We offer stuff ranging from simple on-demand calls to our web service (you purchase credits, docs cost you X credits per access) to a Perl-based app that captures an XML feed and parses and inserts the data into a DB for you to use as you will at your end, usually MySQL but we support MS-SQL too.
We've got some pretty big clients: ESPN, USA Today are amongst them. We supplied Google with Olympic content during the Beijing Olympics.