I love the NXT platform and have quite an investment in sensors and motors, etc. I would like to know if there are alternative controllers that have been integrated with the NXT sensors/motors. By more powerful I mean floating point math, more memory (RAM), more non-volatile storage. Ultimately, I am looking for a way to incorporate a camera onto the brick and do the required image processing.
I would suggest Arduino or, preferably, Raspberry Pi. Here's some info extracted from my previous answer on NXT:
Arduino & Raspberry Pi are flexible development platforms and they can easily be interfaced with other devices. As for image processing the Raspberry Pi would be the better choice since it is more powerful.
RaspberryPi & NXT: Pi is a full computer and very easy to use. To interface with NXT you can use the GPIO pins but thanks to the USB port, somebody already made the NXT-python to control the NXT brick. Being a Linux system you'll probably find some ready-made image processing samples all over the web.