Below are some free materials you can practice online:

• TV shows from the BBC or the news
• A podcast done by someone in a British accent.
• Listening to anything in any accent will improve your listening skills, but a lot of students tell me British accents are harder for them to understand, so based on their feedback I would suggest that when it comes to the exam stick to practicing with British accents.
• The content is not as important as the skill of practicing prediction, targeted listening, recognizing dates, names, numbers, measurements etc,,, so if you have time, let's do some mock IELTS tests recorded in a British/US accent at http://ieltsonlinetests.com.