This isn't really a tutorial since I'm just advising you to install a plugin and giving you some reference html to make it look a tiny bit nicer than it does by default. However I still think this might be useful information for at least a few people so here we go:
Social bookmarking sites like Digg, del.icio.us, StumbleUpon and countless others are very popular with blogs and websites. Becoming popular on one of those sites attracts serious traffic and let's face it, most blogs and websites are always looking to boost traffic. So making it easier for people to "add to del.icio.us or "digg this" seems to be a good idea. By making it easier I mean we'll be adding links for several of the most popular social bookmarking tools to all existing and future entries for a given blog.
To accomplish this we're going to use the Promote This! plugin by Byrne Reese. Download and install the plugin per the directions. Once you've installed the plugin it's time to insert code into the Entry Detail template module. The Promote This! site gives the example of the code for adding a "digg this" link. If you follow that format you'll get a nice text link that works just fine. But if you want to jazz it up a tiny bit you can add the logos for each of the social bookmarking services you want represented.
To get those handy little icons for each service you need to grab either the favicons or other logo button provided by the services. In the code below I'm hotlinking to all the images. I don't recommend you do this, it's just to show you the addresses of all the icons so you can grab them yourself and upload them to your own space.
This code will give you quicklinks to the sites that I've chosen to use/link to. Promote This! supports several other sites so feel free to add and subtract links as you like.
<strong>Share this post:</strong><br/>
<img src="http://digg.com/favicon.ico"><a href="<$MTDiggURL$>">digg</a>
<img src="http://del.icio.us/favicon.ico"><a href="<$MTdeliciousURL$>"> del.icio.us</a>
<img src="http://reallystatic.reddit.com/static/favicon.ico"<a href="<$MTredditURL$>">reddit</a>
<img src="http://www.newsvine.com/favicon.ico"><a href="<$MTNewsvineURL$>">Newsvine</a></td>
<br/><img src="http://www.google.com/favicon.ico"><a href="<$MTGoogleURL$>">Google Bookmark</a>
<img src="http://www.facebook.com/favicon.ico"><a href="<$MTFaceBookURL$>">FaceBook</a>
<img src="http://www.stumbleupon.com/images/icon_su.gif"><a href="<$MTStumbleUponURL$>">Stumble Upon</a>
I've chosen to have links at the end of blog posts, before comments so I've placed the code, in the Entry Detail template module, between