Ran into the need to test different User Agent strings against some PHP code the other day. Fortunately, the excellent User Agent Switcher extension by Chris Pedrick handles this nicely. However, it comes with only 3 agents. Following along with the Yahoo Graded Browser Support guidelines, I needed to test against a wider field of browsers.
Tech Patterns apparently ran into the same issue and put together a sweet XML file with a huge list of browsers. They maintain the list and post updates periodically. It’s good stuff, more than I’d ever need probably. Check it out.