Few beds are heavy and stable enough to stay in place: most move around, however slightly. When you climb in at bedtime, flop over in the middle of the night, or engage in sexy times, your bed shifts along with you. Maybe it squeaks or makes some noise, or, god forbid, bangs against the wall from time to time. Here are a couple of easy and cheap ways to stop the rocking and the knocking...
First off, make sure that, over time, your bolts and screws haven't loosened. If they have, chances are good that your frame has shifted and the parts are rubbing up against each other in weird ways, causing all sorts of trouble. So tighten those first and make sure you bed is nice and secure.
If you have one of those metal frames (sometimes on wheels) that you can buy for $40 off Craigslist or Amazon, place a pair of old socks over the metal ends on each side of the frame. Now, when the frame hits the wall, the socks will not only muffle the noise, but also protect your paint job and prevent scratches or gouges. Of course, any padding will work, but it's a great use for all those random orphan socks that come out of the laundry mysteriously without their mates.
Wooden bed slats underneath the mattress are also notoriously guilty when it comes to generating noise. Hopefully tightening the screws will help on this front. If not, and your bed still squeaks in protest, try wrapping socks around the ends of each slat, providing a nice little cushion for each one to rest upon. Not enough socks? Put some paraffin wax on each of the friction spots.
What's worked for you in the past? How do you stop the squeaking?