http

The article is almost 6 years old but I think it' s nice and worth a read.
Basically it explains how to avoid double POST requests for a HTML form,
and highlights some related caching problems.
You can find it here: http://www.theserverside.com/news/1365146/Redirect-After-Post

I found a very nice command line shortcut today that helped me sniffing http packet headers on a remote server with tshark, the command-line version of the well-known wireshark:

tshark -i eth1 -R 'http' -S -V -l | awk '/^[HL]/ {p=30} /^[^ HL]/ {p=0} /^ / {--p} {if (p>0) print}'

credits: http://andy.wordpress.com/2008/07/10/sniffing-http/