We created an on-line Japanese Text Character Frequency Analyzer tool.
It uses a web service provided by Google.

Intended to help in determining priorities in teaching/learning
Japanese characters (similar to frequency dictionaries, but returns
real-time data and is interactive).

It is free (part of a research project).

Take a look and let us know if it is useful in your particular
situation (we can read feedback in English, Japanese and Chineese).

You can access the tool at the following URL:
http://ispost.massey.ac.nz/kfreq/