If you’re creating Web graphics, then there’s no substitute for Save for Web & Devices. It disposes of non-essential data, reduces file sizes to their absolute minimum, and converts the image to sRGB, the color space of the people.
America likes its lists, and here’s another one. Imaging expert and award-winning author Deke McClelland presents his list of the top 40 features in Photoshop—beginning with #40 and working his way up to #1—one weekly video at a time. Some are tools, others are commands, still others are conceptual. All are invaluable. Learn these 40 features and you’ll know Photoshop.