from my list of ereaders:
Intel (R) Reader for low vision/blind users
BookSense text and audio book reader for Low Vision formats
A friend who has an ipad said they offer white text on black background and maybe a third alternative as well...
I'm legally blind and enjoy the free NLS Bard talking books (tape and digital)
If you haven't heard of it it is a nice service
Recording for the Blind & Dyslexic (RFB&D) offers an online catalog of the best audio book and audio learning opportunities on the internet.
For the disabled, Bookshare leverages the collections of individuals who scan books. Braille books and tools for downloading.
(not free, but some libraries have a small assistance program)
American Foundation for the Blind (AFB)
has forums for technology and books that might be of interest