I've been using WebGuide with Media Center since the initial version, and Doug Berrett has always done a terrific job with it.  But with the newest version, WebGuide 4, he's completely outdone himself.  It's brilliant.  Works great with Vista, has a terrific interface, and it supports on-the-fly transcoding and streaming of recorded and live TV, so I can watch shows from anywhere.  He even has a mobile interface that makes it a piece of cake to schedule and watch recordings from a Smartphone.  Definitely worth checking out.