SpokeMate: Your best friend for calculating spoke length.
A very nice user interface combined with maximum usability. You can select values with predefined fields for very fast input or you can type custom values for every needed data. A quick guide how to measure the hub is also included.
A feature for the next update: Save your calculations und access them without entering the whole data again. In that way you can save your wheels in a very simple way. Thats going to be pretty cool!