Mango Languages 
Mango is an online language-learning system that can help you learn languages like English, Spanish, French, Japanese, Brazilian Portuguese, German, Mandarin, Greek, Italian, Russian and more. The English courses are designed for international students, and include English for Chinese speakers, English for Japanese speakers, English for Vietnamese speakers and more.
English at AMES 
Online course covers the Certificate in Spoken and Written English (CSWE) III and includes modules: Writing for work; Customer Service; Negotiation and problem solving; Job seeking skills; English for health professionals: nurses. This course will help students improve their English language skills through topics relating to their study and work goals such as education and employment in Australia. This is an online self-study course. You can register for any modules and finish it within 6 months.
Road to IELTS (Academic and General)  includes 120 hours of intensive work on vocabulary, reading, writing, listening and speaking, helping students to develop their skills to the levels necessary to succeed in the IELTS exam. It's on trial until 26 April, 2012.
The English Language Skills page offers various resources and information for improving English language skills.