Peekr is a nifty little bookmarklet that you can drag to your browser's toolbar and click on to see a twitter user's entire background graphic and then click again to get things back to normal.
That's it. Pretty simple you say? Yup, and simple is good.
Creating your own Tumblr account view it
We show you how to use your Tumblr dashboard view it
Here are some more ways to post on Tumblr view it
How to browse the Tumblr directory view it
Editing and searching on Tumblr view it
Changing your Tumblr account settings view it
We walk you through how to write a Tumblr post view it