Cognable
Speeka - HTML to MP3 Service
[work in progress]
Developed initially as a Word Press plugin, Speeka now supports conversion of any web pages to MP3 audio using Festival, eSpeak and Mbrola. Once a page is registered with the system, Speeka's crawler regularly checks the page content for changes, updating the audio where it has changed. Page updates are prioritised based on the frequency of audio requests from their domain, but at the moment all pages in the system are easily checked and updated every 24 hours.
Speeka is being developed as a free service and for projects I'm involved with which require particular functionality. Paid for and free ad-sponsored alternatives are already available - if you're looking for something robust and right now - try ReadSpeaker, BrowseAloud [in most non-partisian trials with ID audiences this has come out way on top of alternates, though can be expensive to register for commercial sites] or Odiogo.
If you have a web based project likely to be used by folk with intellectual disabilities and don't mind testing various incarnations as things progress, please drop me a line. It will be 100% available, all that will change is the style of reading while this is being tweaked.
Using Speeka with WordPress requires no work, and its pretty simple to implement on other pages. The service produces an MP3 which can be linked to directly as a simple, accessible solution, although most current applications also use Flash or scripting to play the audio inline.