9. Retouch Tool
The Retouch tool is a drastic improvement upon the older Spot and Patch tool. With two distinct modes, Repair and Clone, you can easily fix most image problems. For both tools, you Option-click to set a source point. With the Repair brush, you can copy a texture from one area and blend it into a destination (preserving color and shading).
The Clone operation performs a much more traditional copy-style operation. Pixels can be painted from one area to another in the image. All of these changes are non-destructive—you can disable all of them or remove individual strokes well after the adjustments have been made.