There are any number of plugins which will handle this for you. However, the simplest might just be do write a bit of HTML and drop it in a text widget which you can then place wherever you want.
Sample html:
<p>You can send me an email <a href="mailto:me@windczar.com">clicking here.</a></p>
Substitute the actual address you want to use. Let me know if you have problems with it.
If you need to know how to format the link, follow this link.
Ken