After thinking about your remarks and my own feelings concerning popups, I would like to withdraw the popup suggestion.
I use Mozilla, and have popups turned off for "All" sites, which I should have considered when making the original suggestion. The times that I have to use IE, they annoy me no end... Plus if the user does want a new window to open there is (in most newer browsers anyway) the option for right-clicking on a link and having it come up in a new tab or window.
I still think a "cheatsheet" of the most commonly used markup and linking information below the text entry box on the input page with a link to a "complete" list of formating and linking information would be a helpful addition to the site.