Take a picture of anything with a small repeating pattern. Preferably set up the perspective so that the size of the pattern as it ends up on the sensor varies accross the picture. This varies the frequency of the pattern on the sensor, which is useful since different effects may appear at different frequencies. It will also help in comparing the cameras since the effects will start at different frequencies depending on the level of optical anti-aliasing in the camera.
One example of such a pattern that should be easy to find is a large brick wall. That has many repeating cycles of the same pattern with reasonable contrast. You can change your distance and/or zoom to get the brick pattern to be different frequencies on your sensor. Take the picture at a angle, and the frequency will change accross the picture.
The best pattern would be a infinite checkerboard. A real checkerboard doesn't have enough patterns to be all that useful. You might find some wallpaper or a large open tiled floor or something. You could possibly print a checkerboard pattern on paper by using 3x3 or 4x4 blocks of printer pixels for each square. That sould provide anough patterns to be a useful aliasing test when framed properly.