We got the Stripology Mini ruler, it is very nice!

On the Stripology Squared Mini Ruler you will find markings to square up half-square triangles, quarter-square triangles, and blocks up to 6" finished. The smaller size makes it easier to wield and makes squaring up blocks a breeze. As always, Creative Grids rulers will glide over fabric until pressure is applied, and then the exclusive grippers will hold the material in place while cutting. The Stripology Mini Quilt Ruler was designed by Gudrun Erla and made in the USA.
Really great ruler!