In my childhood I've watched a cartoon movie which had robots suits like Avatar's war machine.. exactly the same. Help me remembering the name of this cartoon..

Could it be one of the Gundam series (http://www.gundamofficial.com/index2.html)?

There are many similar Japanese anime series and movies with the type of tech you are talking about. The Gundam series spanned a few decades and featured a battle suit version of the big robot characters that looks very similar to the Avatar suit.