Sometimes we discover things whilst mapping that we can't believe we ever lived without. These barely-documented featurettes of design software can completely change a workflow, so if you think you know a cool tip for modders, share it here.
To make the thread easy to read at a glance, mark your tips with this arrow symbol: http://hunter.weebitmagic.com/gfx/linkies/greenarrow.png (using simg tags) to separate discussion from tips.
I'll start us off with an unbelievably handy photoshop tip that, mind blowingly, most people don't seem to know about:
To select a layer in photoshop perfectly; that is with its exact alpha values and little pernickity stray pixels, simply ctrl+click the layer's thumbnail in your layer list. Ctrl+shift to select multiple layers.