I wanted to try and learn ARM NEON.  After a lot of looking, I decided to try
and implement a few basic image processing algorithms, optimized for neon.
The nicest image processing library that I could find to work with was Python's
PIL.  A good share of that library is written in platform independent C.
The plan for argon is to implement some of the ImageOps, ImageStats, and
ImageFilters found in PIL, optimized for NEON.

A couple of nice NEON resources/reads:
http://gcc.gnu.org/onlinedocs/gcc/ARM-NEON-Intrinsics.html
(gcc page on NEON intrinsics).
http://blogs.arm.com/software-enablement/161-coding-for-neon-part-1-load-and-stores/
http://blogs.arm.com/software-enablement/196-coding-for-neon-part-2-dealing-with-leftovers/ 
http://blogs.arm.com/software-enablement/241-coding-for-neon-part-3-matrix-multiplication/
(Series of tutorials on programming for NEON).