On: Netcat – The swiss army knife of networking

[stiff]

Ngrep is another awesome tool that is a networking equivalent of a common UNIX utility (although a more loose one in this case):

http://ngrep.sourceforge.net/

Also +1 for socat as a netcat replacement, having SSL there when needed is really helpful. I use it a lot for testing when developing network applications, replacing one end point with a fixed set of responses or even typing stuff in interactively etc.