Lately I have been working allot with inductors, ex: DC/DC converters and had a problem not knowing the inductance of most coils I worked with so I decided to build an inductance meter using Arduino and LM393 Comparator. I found the AVR LC meter with frequency measurement project by Kerry D. Wong very helpful, it made me understand the concept behind the measurement . The schematic and Arduino code based on similar project by ReiBot.org. This meter is not very accurate compared with profesional ones but it does the job.
Update: A better Arduino sketch by ultimoistante: code here.
Using iCircuit App for iPhone