I am currently working on various preformance optimizations for the OpenJPEG JPEG2000 library. Here you can get snapshots of what I did so far. This is work in progress, and not suitable for using it in applications. Read the README.quickOpenJPEG for more information.
If you're looking for a stable version: I am in contact with the authors of the OpenJPEG library to find a way to backfold my changes into their library (mainly, we have the problem to solve that I used C++ and they don't want to depend on C++ in their library). Once the changes are in the official version, you will have the stability and reliability of OpenJPEG, just faster.
Downloadable snapshots of my sources:
Cost estimation of quickOpenJPEG-20070122 produced with callgrind and kcachegrind for decoding a test image on Linux/AMD64: