Even in this digital age, I'm still using Polaroid to evaluate my photos before committing them to pixels. I have been using a portable DVD player made by Polaroid Corporation attached to my Nikon D2X. I'm sure their are several brands of portable DVD players to choose from. I use Bogan Super Clamps to attach the DVD player to my tripod. I usually only use this set-up when am lighting or their are other at the shoot that need to see a more detailed preview.
This system works well for me, I hope it does for you.