You can install the Advanced Logging module for IIS 7. Once installed you have the option to define new fields from several different sources. One of those sources is other modules.
What I am unable to figure out is how to get a list of the fields that the other modules 'publish'. There a boat load of modules installed by default and I have to imagine they are publishing some data I would care to know about (hopefully UrlRoutingModule publishes what I'm specifically looking for).
Also as an aside if you know how to or know where good documentation on writing .net HttpModules that publish custom fields I'd love to see/hear about it.