Ship or Sheep is a useful website for practising pronunciation. This site focuses solely on minimal pairs. Minimal pairs are words that vary by a single sound. On this very simple site, you can listen to minimal pairs for many different sounds. First click on a pair from the chart on the homepage. Then mouse over the words to hear them. You will hear male and female voices in British English.
The pairs also have pictures in case you aren’t familiar with the vocabulary. As you study minimal pairs, you can also learn the IPA symbols. This will help you understand the pronunciation of a word that you find in a dictionary. To use this site, you will need audio and Flash.