Httest is quite a nice tool for various of things:
Scriptable HTTP Test Tool for testing and benchmarking web application and web server development without GUI.
Special: Can act as client (requesting) and server (backend for reverse proxys). Pattern matching answers (both server(s)and client(s)) to test validity. You are completly free in what headers you like to send (good and bad ones) and what content. Can exectute any shell command you like and stream the standard output back to the HTTP stream.
I created the Windows build, you can download the project file for MS Visual c++ Express: