So here's the scoop. The cover for the Review measures 5.5" x 8.5". If you want to include the back cover, its obviously will be the same size, but also compensate for a roughly .25" spine which typically is just text.
I'll ad the covers from past issues between last year and 2001-ish. Sorry for the questionable photos, only had my webcam.
Make sure any submissions are print-quality. 300 dpi.