create or define HTTP monitored resources

Tim and I were discussing the other day the need for uniform, unchanging monitored resources over HTTP. Currently, monitoring the apps over HTTP is bit of moving target. Often times a sensor will fail not because there is a problem, but the state of the application has changed. This has forced us to lower the bar to the most basic pages and search strings available, which means that sometimes we can miss real problems.

What I'm after is a single resource in every application accessible over HTTP that:

1) tests the application is working properly using any method that makes sense
2) does not require login
3) will never redirect anywhere
4) does not depend on another application
5) works the same on gapps and non-gapps
6) works the same on for unauthorized gapps (redirect to gapp domain)