[jase (Jason)]

RE-selections
Control + D can be used to deselect an area or selection criteria. However something pretty cool is the the reselect feature - Control + Shift + D. PS will only remember the last selection criteria.

Drag Selections (oops - just realised I've already mentioned this in post #9)
This works really well if you want to chase filter reflections or star halos for what ever reason. Use the selection tool of choice, typically the Elliptical Marquee Tool (hot key - Shift + M twice), select the halo or reflection, before releasing the left mouse button, hold down the spacebar to move the selection around - release the spacebar to resize the selection if desired. This will allow you to precisely select the reflection/halo and unselect the star to form a "donut" selection to ensure specific processing does not alter the stellar profile.

Zoomie Zoom
Control + Alt + mouse scroll wheel up or down to zoom in or out respectively. Also, double clicking the magnifying glass (zoom) button in the tools palette is a quick way of zooming to 100% (1:1).

Brush size and hardness
Mentioned in a previous post, the [ ] (square bracket) keys alter the brush size...an extension to this is the hardness of the brush. This can be altered by pushing Shift + [ or ] to alter on the fly. I don't alter hardness often, but it is useful.

Supafast layer opacity adjustments
This is not really a tip, but I use it all the time as its a time saver compared to fluffing around with the mouse. Select the layer you want to change the opacity on, say a rich Ha data set that when blended at 100% is too rich for the RGB data. Simply use the numerical key pad to enter the opacity value. 1 = 10%...9 = 90%. If you type specific numbers in quick succession, say press 4 then 5, the opacity will be 45%. Too logical huh?

Tool-less view
If you're working on a system with a restricted desktop resolution and you find you're for ever scrolling about and shift tool palettes to get a better view of the image you're working on, simply hit the TAB key to hide them, hit it again to bring them back. This is a cheaper option than setting up a dual display graphics station where you have one monitor for the image and the other for your tools.

OK, here's one from my friend the Pixel Princess (had better give credit where its due as this is cool, well I think so as I've used it a few times).

Visible layers into a single new layer (w/out flattening of other layers)
In the layers, select the layers you'd like visible i.e. have the "eye" beside them. For example, an Luminance and RGB data set. Then press Control + Alt + Shift + E. This will merge the visible layers into a new layer while still leaving the original layers intact. You can then go on to use a hard stretch, saturation pump up activated as softlight blend for a LRGB colour boost.

Enjoy!