I usually crop them one-by-one to retain the control of the cropping area. Instead of using PS, I use JPEGCrops (http://ekot.dk/programmer/JPEGCrops/) - very simple and effective tool for cropping before printing.
back in the film days u just send in your negatives or slides for prints, whether it's 3R or 10R. you don't resize your negatives or slides then. similarly, for digital, you could just send in your highest quality images for prints.
cropping though is another issue. it is to ensure that you get the right details in the final prints.
Backup all images to DVD or CD.
Resize the less satisfactory images (70%?) to lower res
Delete the high res copy
Only reserve the high res "keepers" in harddisk for immediate reference.