Mac users have longed wished that the Finder would implement a very simple feature: cut and paste. It hasn't happened yet, but you can easily add that feature with a handy app called MoveAddict.
MoveAddict lives in your OS X menubar, providing you with easy access to your new cut and paste options. Of course, you can also use the expected shortcuts (Command+X for cut and Command+V for paste) anywhere in the Finder. If that's not enough, it will add cut and paste toolbar items that you can add to Finder windows.
Using MoveAddict was a little confusing at first because it applied a blue label to anything I cut (rather than removing it). When you cut a file, it doesn't immediately disappear to be stored in your clipboard. Instead, when you paste the file it's moved to the new location. While this isn't true cut and paste, the effect is the same. (Oz LH ed notes: This is the same approach Windows has always taken, and it eliminates the theoretical worry that you might lose a file if you cut it and forget to paste it.
MoveAddict will run you $US8, but you can use it for free forever with the limitation of only being able to cut and paste one file at a time. Unless you plan to cut and paste batches of files frequently, this is a pretty easy limitation to live with if you're not in the mood to shell out $US8. Previously mentioned TotalFinder also adds cut and paste, plus a bunch of other features, but costs twice as much and only lets you use it for free for 14 days.