Ttytter:

A Twitter client for the command line written in perl, it’s an entirely self-contained script so if you take it’s executable and the config file in your home dir, you can use it over ssh or from anywhere!

http://www.floodgap.com/software/ttytter/

Irssi:

This one is a far more well known client, but I still love it to bits and I use it every day. Also, if you don’t know what IRC is then checkout en.wikipedia.org/irc

http://irssi.org/

Google:

I am sure that many of you aren’t aware of this, but Google has provided its suite of CLI commands for everything from contacts to picasa to the public. Originally it was intended for Google employees but now we can all have access! really handy for quickly checking something or doing some basic (but often important) tasks while X windows is down or your on a server or something over SSH.

http://code.google.com/p/googlecl/

Todo.txt

This one is both a command line and a text file todo system.

I’ve been using it for a few weeks so far and I really love it. It’s simplicity and extednability is wonderful, with clients for both android and iOS that sync via Dropbox (My preferred method) I think that todo.txt is really wonderful, and I recommend it for any CLI buffs that are looking for a greener pasture in the todo list scene.

http://todotxt.com/