Do you need to practice more than one skill? Start with one of these links:
LiveMocha - online language learning committee
Smart.FM - General language learning site
BBC Learning English – This website is a good place to improve your listening, reading, vocabulary, and grammar skills by using some latest BBC news. It also provides vocabulary definitions to help you learn new words.
English at Home - English-at-home can help with grammar, vocabulary, idioms, punctuation and more.
English Baby! - Join the student community at English Baby! You can learn new vocabulary, slang, and informal American English with the free resources provided here.
The Cambridge Advanced Learner’s Dictionary - The Cambridge Advanced Learner’s Dictionary gives definitions and examples of word use, as well as worksheets to help you learn new words.
Learn English—British Council - Songs, games, grammar and more. Check out the archive for lots of English language learning materials.