This is a quick introduction to some neglected filters in PS. Thry them out and have fun!
MEDIAN is a filter that averages the colours, pixel after pixel. It is used to remove noise. When you use it on clouds, your shapes will become more uniform than with Gaussian Blur. Visually, it gives a more molded effect.
It also creates edges instead of blurring them. So you can still use an unsharp mask after applying Median.
HIGH PASS is a filter that greys your image out where there are no edges to be found. The edges stay intact. It is very handy to accentuate edges, even more when used with a separate channel because some channels accentuate the edges by themselves already. It is also very handy before using the Threshold command.
Try this: duplicate your background image, apply HighPass to the duplicate and blend with HardLight. This is a great way to sharpen images.
MAXIMUM AND MINIMUM are filters that oppose eachother. MAXIMUM expands the light portions of an image, and MINIMUM the dark portions. The setting tells PS how many pixels you want to expand(maximum) or shrink (minimum) the lights. Both are incredibly handy on Alpha channels and masks.
Neglected jewels 
Linear Mode
