This site, washingtonpost.com's U.S. Congress Votes Database, is a deep database of every vote in the United States Congress since the 102nd Congress (1991). It lets you browse votes in a variety of ways -- both in aggregate and for individual members of Congress.
This site publishes an RSS feed of recent votes by each member of Congress, and a feed of the most recent votes in both chambers. See the RSS page for full details.
This site is generally updated every day, although there is a delay between a vote in Congress and its appearance on the official Congress Web sites.