There are two things you want to make sure each of your posts have.
First, a simple tool to allow your visitors to share your post with others. This started out as a tool to merely email the article to a friend. Now there are many plugins to WordPress and other cut and paste solutions to provide your visitors with this capability.
Second, the ability for your visitors to bookmark and submit your article to delicious, digg, facebook, technorati or other website, is a must as well.
My favorite you will see next to the title of this post from Madkast. They allow you to not only email to a friend but also send to their phone by using a phone number. Implementation is also easy as you merely enter your email address and cut and paste code they provide you. This means that you do not need to ftp anything to a server, you merely paste the code they provide once and you are done.
Take a look at the Madkast link next to the title of the article in the screenshot below, and the white overlay shows the window that pops up and all the features your users will have.