Cambridgeenglishonline  - (Full name - Cambridge English On-line) is a very useful site which includes:
- A wide selection of phonetics resources - including on-line activities and printable charts.
- A free flashcard maker
- Some English Idiom activities.
The most well-developed part of the site is the phonetics resources which are really quite good. The on-line phonetics games can be quite addictive.