WWAAC (seen left top)
Has: integrated speech (tts and talking buttons), some picture symbol support, summarize feature to lower cognitive load, customizable interface using layout editor
Access Methods: mouse, mouse emulator, switch scanning (one or two), touch screen
OS: not specified on their web site
(seen left bottom)
Has: tts/talking buttons, full symbol support (you must use free software to integrate your own picture symbol set), simple interface to lower cognitive load, comprehensive manual for download
Access methods: mouse, touch screen, mouse emulator, switch scanning (one or two) with Grid Editor add on software (free)
OS: Windows 98-XP
Notes: it takes a bit of effort and set up to get EdWeb the way you want it, but once you do it is great! Also it works with the free EdWord symbol/talking word processor and the free software to integrate your symbol set and create grids (like Clicker 4/5 or Classroom Suite)
Has: tts, enlarged print, highlight text, talking buttons, customizable interface
Does not have: picture symbol support
Access method: mouse, joystick, touch screen, switch scanning
Notes: works with Multi Mail e-mail program
Don't forget that Firefox and Opera have many, many options to make them more accessible such as the Firefox Accessibility Tool Bar and Click, Speak.
And I did not include any of the many free accessible browsers for users who are Blind/Visually Impaired, like WebbIE, please use Google or search OATsoft to find these if that is what you need.
Some photo editing for this post was done with the free Pixenate Web 2.0 application.