Unfortunately there is no direct way to sort gmail messages by Size, Sender, Labels, Subject. However, Abhishek has written a detailed report on how to achieve this using some workaround techniques.
And the rest of us, we should suggest Google to include this feature :
1. Login to your GMail account and click “help” and under “Help resources” click “Suggest a Feature” (or you can directly do it by going to “http://mail.google.com/support/bin/static.py?page=suggestions.cs&issue=116865&bucket=16935“)
2. You’ll find “Organization” section, click “Suggest it” for “Sort messages by size, date, sender, etc.”
You can use http://www.findbigmail.com to label your big emails into three groups so that you can go through them and delete all the ones you no longer need.
It uses Google’s third party Oauth interface so you do not have to share your password to use it.