CamTimer is a camera timer app designed to be as simple and efficient as possible. Just set the delay to 5, 15, or 30 seconds and press the shutter button to start the timer; at 3 seconds remaining you'll hear beeps, and then the picture will be saved. After you take a picture it will be shown full screen, allowing you to share or delete it.
You can also take 4 pictures in succession, control the camera flash setting, switch to the front-facing camera if available (requires Android 2.3 or later), and take pictures without a delay.
CamTimer is now completely free and open source. You can get the source code at https://github.com/dozingcat/CamTimer.