Ooooh, they come by the dozens !!

At least, that's what I notice when I teach or present old or new Photoshop features to advanced" users. They often slap their heads for not knowing many of them all the time...

My favourite Top 3 to give away:

1. The Perspective CropVery useful for straightening posters, paintings, pages, or facades, you've captured by not standing right in from of it but a bit from the side. It prevents a reflection of yourself, the flash, or anything else obtrusive in the environment.
2. The Magic EraserCome one, this is a simple one you can't miss. In stead of using the Magic Wand to select a background color, hit Delete, wait for Content Aware to erratically fill the surrounding with 12 sheeps or whatever you'd like to cutout, Undo, turn the Background layer into a real layer by unlocking it, hit Delete again, and choose Delete None, you could simply have touched the background with the Magic Eraser – presto ! And yes, it has a tolerance setting.
3. The Smudge FingerReally ? Really, it can serve a serious purpose. Imagine a tightly cutout object on a separate layer, cut from its environment. But although the shape looks okay (maybe selected by path, Quick Select, Quick Mask, or anything else), there are still some remnants of the background's content and color in the fringes. Lock the layer's Transparency, set the Smudge to a large and medium soft edge, and carefully drag the inside's content a few pixels outwards, beyond the edge of the shape. The lock ensures that the shape won't become a stretched blob.

Oorspronkelijk geplaatst op Quora: What is a Photoshop tool or function that you didn't know was there for far too long?"