Press Tab will hide tool bar and palette, Shift+Tab will hide only palette.
Hold Shift + click the top blue bar for toolbar and palette will move them to the nearest edge.
Double click the top blue bar, on any palette window, to minimize it.
Double click the gray background will bring up open file option, Hold Shift+double click will open up the browser.
Sick of the default gray background around your image? Select paint bucket, hold shift and click on the gray background, it will change to whatever color you have in your foreground color box.
In Photoshop, all "Cancel" buttons in a window can be changed to a "Reset" button by holding Alt.
Caps lock will switch your cursor for accuracy.
Press F button, it will switch between 3 different screen modes and give you more working area.
To draw a straight line, click then move to the end point and hold shift + click.
Hold Ctrl will temporary make any tool into move tool until you release Ctrl.
Ctrl + Alt and click drag the image, it will make a duplication of the current image over lay on top.
Hold Space bar, it will make any tool into "Hand Tool" until you release Space bar.
While in Zoom Tool, Ctrl+space = zoom in, alt+space = zoom out.
Hold Ctrl and press "+" or "-" it will change the % for image in navigator window.
When Using eyedropper tool to capture foreground color, hold Alt and click, it will instantly capture the color for background.
With Measure Tool, draw a line then hold Alt and draw another line from the end of the first line, it will measure the angle.
Ctrl+Alt+Z and Ctrl+Shift+Z will go back and forth in the history.
Alt+Backspace and Ctrl+Backspace will fill in the whole screen with foreground color or background color, Shift+backspace will bring up option window, Alt+Shift+Backspace and Ctrl+Shift+Backspace, will fill the image with foreground or background color but will leave the alpha transparent area alone.
When free transforming with Ctrl+T, hold Alt to keep the original image and then to transform a duplicated layer of it. Ctrl+Shift+T to repeat whatever you did in the last transform.
To make sure your Crop is on the edge of the image, hold Ctrl while cropping.
Ctrl+J will duplicate the current layer.
Ctrl+Shift+E will merge all visible layers to one layer, Ctrl+Shift+Alt+E will make a copy of the original and merge all visible layers.
While using Marquee Tools, hold Alt it will make the starting point as a center of the selection.
Ctrl + D to deselect, Ctrl+Shift+D to reselect what you deselected.
While selecting with Marquee tool, pressing the space bar can allow you to move the selection.
Hold Alt while clicking on the eye icon beside the layer, it will hide all other layers.
Hold Alt while clicking the pen icon beside the layer, it will unchain this layer from all layers.
Select a layer, hold Alt and click the top edge of another layer, it will group them.
File> Automate > Contact Sheet: this can create a small thumbnail for every file, this can save you some time from searching.
After, draw a path on the image with pen tool, Ctrl+shift+H can hide/show it.
Ctrl+Tab allows you to switch between different image files you are working on.
F12 = Revert to how the file was the last time you saved it.
Holding Shift + Alt while transforming an object will do it proportionally, from the center.
To center an image, Ctrl + A , Ctrl + X, Ctrl + V, I think it also puts that image on a new layer.
Ctrl+E will merge the highlighted layer down to the next
When you have a brush selected, using [ or ] will scroll up or down that brush list.
Double clicking the zoom tool will make the image 100%, double clicking the hand tool will fit the image to your screen resolution.
Ctrl + Alt + T to make a copy of the layer in which you want to transform.
Ctrl + Alt + Right arrow. duplicates the layer you are on.
Ctrl+[plus key] will let you zoom in on an image anytime while Ctrl+[minus key] zooms out. Ctrl+Alt+[plus key] will zoom in AND RESIZE the window to fit the image size... same for Ctrl+Alt+[minus key] as well.
Pressing X will switch the selected foreground and background colors.
Pressing D will reset the foreground and backgrounds colors to black and white.
Ctrl+Alt+Z will do multiple undo, versus just one.
Ctrl+click a layer thumbnail to select the layer transparency
To see what your layer mask looks like (and edit it), Alt+click its thumbnail in the layers palette
When using Polygon lasso tool hold Shift to make a perfect line, it goes every 30 degrees
Stamp Tool (s) is used to copy an area of image (defined by alt+clicking and area) and paint it somewhere else (cloning). It also works when you have multiple images open at the same time. Alt click an area of any opened file image and paint it anywhere else.
And remember, pressing enter when you type will take you to a new line just like typing a letter but pressing Ctrl+Enter or Enter on numeric key will finish what you type.
Pressing Tab key will hide the Tools palette and any other palette that you have on the stage. Pressing "F" will change between Full Screen modes. Using these two tips you can view your work Full Screen without any palettes.(You can press CTL+Alt+0 to fit your work to the screen, or you can press CTL+0 to zoom to 100%)
Pressing the "+" and "-" keys while holding down CTL+Alt will resize the whole document window, not just the work area.
Ctrl+click a layer (in layers palette) to select it's transparency.
Ctrl+Alt+click between 2 layers in the palette to group them.
If you have a mini scroll on your mouse, you may use that to zoom in (scroll up) or zoom out (scroll down).