When saving a file, and you want to put it onto the Desktop but you’re looking at some other folder, press ⌘-Shift-D and you’ll go straight to the Desktop. Also, when you’re in the Finder, and looking at a Finder window, and you want to see the stuff behind it (on the Desktop), don’t bother with shoving windows out of the way so you can see the Desktop. Instead, do ⌘-Shift-D and the window you’re looking at will display the Desktop’s contents. Switch to Icon View (⌘-1) if you want, but List View (⌘-2) is faster since you can sort by name, date, etc.
Note: ⌘-Shift-D does other things in other programs. If Mail is frontmost, ⌘-Shift-D will Send the message you’re writing. If Safari is frontmost, the web page you’re looking at will go to your Reading List. Be sure you’re either in a Save… dialog box or in the Finder before trying the ⌘-Shift-D thing.