HST rulers
 

I saw this ruler somewhere but don't remember where. Using the Thangles it squares up the blocks before you open them up. I like using the papers but have trouble with keeping them all the same size and would love the ruler.

I've always just used a regular ruler when cutting apart the Thangles - if you cut on the lines all the HST will be the same size.

http://quiltbug.com/articles/half-square-triangles.htm

Is this what you are looking for?

I believe Eleanor Burns has a ruler for squaring up before opening them.

Just checked out the Wonder cut ruler and ordered one. I can't wait to try it!