This free sound editor works on Mac and Windows; you need the LAME add-on to export mp3 in Windows. I have used this program for several years to change tempos and edit dance music.
Text to speech site that accepts typed text, uploaded Word and .pdf files and creates an audio with a talking avatar. You can then download as mp3, podcast, email. Free account is limited to 30 second recordings but special teacher package is available.
SpokenText converts any text into clear natural sounding speech. Free account lets you paste in text or convert a webpage and either store it online for 7 days or export in several different formats including mp3 and ipod. Works great!