I picked up a great little rotary made by Carl a couple of months ago. Metal base, holds the paper securely flat while cutting and was very inexpensive. The drawback? It only cuts up to 12". It works wonderfully for my 8x10s and cutting test strips in the darkroom but that's about it. Apparently there are 15" and 18" versions and also other models but I haven't tried them.

WARNING! My last rotary was an X acto with a plastic base. It was awful. It didn't flatten the paper under the blade very well and the base tended to flex under pressure and cause the cuts to vary. Mercifully, the thing fell apart within a year of light use and I was able to do to it what I should have done to it as soon as I brought it home. It would have saved me some aggravation.