HTTP Archive : The HTTP Archive tracks how the Web is built.
HTTPie : HTTPie—aitch-tee-tee-pie—is a command line HTTP client with an intuitive UI, JSON support, syntax highlighting, wget-like downloads, plugins, and more
HttpWatch : An HTTP Viewer and HTTP Sniffer for IE and Firefox
RequestBin : RequestBin gives you a URL that will collect requests made to it and let you inspect them in a human-friendly way.
Use RequestBin to see what your HTT...
httpbin.org : A simple HTTP Request & Response Service.
