These are links I've found so far that are very usefull for Twitter users, you can make some extra cash, advertise with them. I'm still experimenting with all of them to find their full potential.

Join the Twitter explosion. Twitter is fast becoming the place to catch up with friends, but more and more it's the place to advertise your products to your followers. The more followers the bigger your potential. I am very new to this and will be adding updates as I go on my Twitter journey. So if you do "Tweet" come back to this page every now and then to see if there are any new links you could use.