This video by Michael Ninnis was taken at this year's Adobe Max, and IMO one of the best and most useful Photoshop tutorials I have ever seen. No matter how well you know Photoshop, I bet you'll learn some really cool tricks and tips from this.
BTW I think he was on drugs when he took the class, but bear with his OTT delivery. It's worth it.
[video]http://tv.adobe.com/watch/max-2013/photoshop-power-shortcuts/[/video]
Right after using keyboard shortcuts, the most useful thing from a productivity point of view (IMHO) is custom work spaces, and to make them really work for you, you need two monitors. It is liberating being able to instantly access the Paths panel to load a selection by Ctrl (Cmd) clicking a workpath. The same thing goes for having the Brush panel always available. So getting this back on topic for the thread, does everyone know that you can save your customized keyboard shortcuts with your work spaces? Another tip, and this is one of mine and not in the above tutorial, is to remove the shortcut from rarely used tools. For instance I never use the Sponge tool, but constantly use Dodge and Burn, so with the short cut removed from the Sponge tool, I can toggle between Dodge and Burn with Shift o. Others I have removed are the Slice tools, most of the eye dropper fly out options, half the brush tool options, 3D materials, and the Sharpen tool.
I bet there are some tools you never ever use? I never use the History brush, for instance, so I have stolen the 'y' shortcut for the Blur and Smudge tools, which don't come with shortcuts by default.
Hope this helps