iLEVELi for iPhone

From Directed Graph Software:

iLEVELi simulates a bubble in a fluid to provide a versatile inclinometer with an intuitive user interface. It displays its angle measurement continuously, in landscape and portrait modes, and when laid flat. A catch-and-release method prevents screen touches from perturbing its measurements. Press the "Catch" button, and the bubble settles before the measurement is captured. Press again to release and resume angle tracking. iLEVELi can correct the accelerometer's gain and offset errors in three dimensions. Its more comprehensive calibration delivers better measurement accuracy, especially on slopes. Calibration takes about 90 seconds. A built-in guide leads you through it.