I found the Yahoo! FareChase Alerts widget the other day. It looked promising, but upon reading the comments, I didn't want to bother downloading it
If you check out the ProjectVRM website, you'll see that VRM is all about "providing customers with tools for engaging with vendors in ways that work for both parties".
The VRM wiki specifies a requirement for a Firefox plugin. With the help of Ian Bugeja and his HyperBK tool, we had a go at creating a plug-in that allowed a user to crudely specify their needs and publish those as Machine Readable APML. You'll find this at the Xpollen.org website.
Where we go from here...watch this space!