I'll add one of my favorite ones: you can do Option-Command-C to copy the path of a file to the clipboard (if you need to use it somewhere that doesn't support dragging to paste a path).
To add to this marvellous shortcut I will now be using very frequently:
Right click on the file in finder, then hold the Option key and you'll see the copy command change from "Copy [file]" to "Copy [file] as Pathname".