I have a Fiskars 12" Rotary Trimmer:
This has worked well for my trimming as well for my wife's scrapbooking projects on 12" square papers. I happened to get mine at Michael's (an arts and crafts store) for about $40. What is neat about it is because you can change the blades out to either a patterned edge cut or a scoring blade. I have used the scoring blade on some 5x7 paper to cleanly fold over to a notecard with a picture on the front.
I want to step up to the 24" model because I have the i9100 printer (13x19 prints) that I may need to trim down.