Evil Mad Scientist Labs posted a thorough update to their accelerometer tutorial using ADXL335 breakout board, ATMega168 chip, and LEDs as indicators –
The big idea is that when there is no acceleration in (say) the X-axis direction, both X-axis LEDs are off. When it detects acceleration one way, the red LED lights up (and brighter, the higher the acceleration is) and it lights up blue for acceleration in the opposite direction. (Naturally, the other two axes work the same way.)
The full step-by-step + source code can be found on EMSL’s site.