72 for web and computer graphics, 300 for print. Monitors, to my knowledge, can't display anything higher than 72 anyway (that's what one of my teachers said, anyway). Printers tend to print at 300dpi, which is why you want your resolution set to that if you're printing.
/thread thanks socsaint, i needed to know that too. I'm sick of printing my images without having to be cropped or anything, but they still come out looking like ----.