Well, everybody else already knew it, but in most video programs the space bar will pause and play. (It’s really embaressing that I didn’t know that because my boyfriend of three years owns his own video production business, but I only found out about the space bar a month or so ago. He mocked me mercilessly.)
In Adobe Illustrator & Photoshop (and probably the other CS programs), ctrl-0 will make the image fill the screen. Ctrl-1 will zoom to 100%. It works in CS & CS2, I don’t know about older than that.