Pronunciation of the -ed ending Explanations and exercises by michelle, including 2 pages of useful sentences with their audio
Pronunciation of the -ed ending 02 - more stuff plus links to on-line exercises
Phonetics in the Classroom: Phonetics 01 (1 page)
Understanding the vowels (4 pages) by michelle (2006)

Are you good at hearing the vowels?
The Vowel Machine : listen and pick the spelling! 1. Click SPELLING. 2. Click SPIN. 3. Choose 1, 2 or 3. 4. Check result below. 5. SPIN again! Do it 100 times, till you get them all right!

Perfect Pronunciation Exercises (US American)
Practice Pronunciation with the BBC (British English)
Tongue Twisters
Pronunciation Poem at the British Council

Dictionary with audios: Merriam-Webster On-line (English-English). Click on the loudspeaker and you'll listen to the pronunciation of the word (US American).
Pronunciation differences US/UK Englishes
Sounds familiar? Accents and dialects of the UK (British Library) Link sent by Gonzalo (Y5, 2007-08)

AN AMAZING EXTERNAL LINK: Learn how sounds sound!, their transcription, and more things! Click on the Lauch English Library (on the right of the screen) and learn it all about the phonemic system!