I haven't used them, but laser level squares from the hardware store seem ideal for squaring up quilts for trimming and blocking. Here is a tutorial on how to use them:
http://www.dreamweavers-quilts.com/q...hort-tutorial/
Oh, and I just remembered the spring clamps I bought at Menards over the weekend, for clamping layers when I spray baste. These open 3 inches wide and have a ratcheting mechanism with a trigger; very easy to both open and close.