Rather than paying good money to buy a ceiling mount for my projector, I decided to make my own, DIY style. If you are interested in buying one yourself (not from me; I'm not selling anything), click one of the pictures below and then check the links at the top of the page for prices.
This one is pretty simple to make, as the pictures show. Getting it properly positioned is the trickiest part. You have to do your best to aim the ceiling board up perpendicular to the screen before you screw everything in. If you don't get it lined up right, you can gouge out the drilled holes that the downward facing bolts go through to give yourself some adjustability.
For aiming up and down, you just have to buy bolts that have a little bit of extra distance, and you can adjust the tightness of the butterfly nut. If you need to aim the projector up, tighten the nuts at the front more and let the butterfly nuts in the back hang looser. Gravity takes care of the rest.
Then, a few coats of paint to make it blend in better, and it's done.
This system also let's me take the projector to other places quiet easily. I just unscrew the butterfly nuts and take the projector with me. I never even need to remove the board that is attached to the projector.
If you have any comments, feel free to add them to the pictures.