Who can help me... I need to improve my English because I study languages at the University and my colleagues know English perfectly... someone for there?
http://www.conversationexchange.com - you create an account and then search for practice partners. You can search by various criteria such as gender, age, nationality, hobbies. You can search for pen pals, audio chat partners, or video chat partners. You can use their internal messaging service if you don't want to give out your email address.
Also check out iTalki, weSpeke, Busuu, HelloTalk, Tandem, and goSpeaky.