1. What's your name?
Put your name first. Use your first and last name as people usually address you.
2. Who do you work for?
Make sure you include your company name. Don't make readers guess at who you work for. If you want them to know you, then make it easy by providing the information in your email signature.
3. Where are you from?
Include an address, complete with a zip code. Even though we operate in this wonderful world of technology, sometimes there is an occasion to send something to someone via snail mail. The easier you make it for someone to contact you, the higher the odds that they will.
4. Where on the web?
If you have a website address, make sure to include it. While it's nice to list it cleanly as www.mycompanyname.com, not all web browsers will be able to click on that link and be directed to your website. To mitigate that problem, try listing your company as http://www.mycompanyname.com.
5. Call any time.
Make sure that you include all the telephone numbers at which you can be contacted. Write them out completely as they should be dialed.
Your email signature is more important than you might think. People are busy; when they need or want to contact you, make sure they can find the information quickly and effortlessly. Otherwise, you risk the possibility that they will close out your email thinking they will get back to it at a future time which ends up never materializing. Or even worse, they will contact someone else who has provided their information in a more useful presentation. 