If you are into making videos here are some keyboard shortcuts that work the same across many video editing programs including Final Cut Pro, iMovie, Adobe Premiere Pro and Adobe Premiere Elements. I find that they speed up how I work particularly when playing back and reviewing clips or the time line. You do need to make sure that the clip or timeline is selected.
Space bar = play and pause. Each time you press this is will either play or pause. Works on lots of software including QuickTime, VLC, Windows Media and all the video editing software I mentioned above.
L = fast forward. First time you press it if the video is paused it will play the video, each time you press it after that it will fast forward faster until is hits the maximum speed. The space bar stops it fast forwarding.
J = rewind. Each time you press it it rewinds faster up to the maximum speed. The space bar stops it rewinding.
Right arrow = moves play head forward one frame at a time.
Left arrow = move play head one frame at a time backwards.
I = in point. This selects the in point of a clip.
O = out point. This selects the out point of a clip.