The following way I am using is to add the Digg This button to every post by modifying the template.
I guess I'm supposed to say here that you should save your template to your hard drive before modifying it. I haven't done that yet, but it's up to you.
So, Go to your dashboard, click the Template tab, then Edit HTML.
Click "Expand Widget Template"
You will need to find this piece of code:
It is about half way down. (tip: you can search the page in firefox and explorer on the mac by typing "apple" "f" and on Windows by typing "ctrl" "f", then typing "data:post.body" and it should find it.
Then copy the code below this sentence and replace the above piece of code completely (take a good look at this code, you can see it adds the replaced code back in)
Now, understand this...this code will add a button to all your posts with a "zero" diggs displaying until someone diggs it, and so, you can go and digg your stories first, or wait until one of your readers do it.
The Digg This button will be placed "align=right", top right corner of your post, so if you tend to put large pictures opening your post, you might want to make them smaller (less width).