This is something that has bothered me a lot recently as I have been using Photoshop for Wedding photo’s and this and that, and this tool would I’m sure save countless designers some time, especially if your not hot on file naming conventions.
http://lifehacker.com/5302051/thumbview-adds-thumbnail-support-for-unsupported-images
The idea is to allow Windows to thumbnail up to 19 additional image formats including PNG, PSD and TIFF to name a few.
I haven’t personally tried it yet, but the nice people at Lifehacker claim it was fast and didn’t cause a performance hit which is what we like to hear.