Graph Your Inbox is a nice Google Chrome extension that shows interesting stats about your Gmail account. The extension lets you type one or more queries and plots the results on a graph. The nice thing about this extension is that you can click on one of the datapoints to view the corresponding Gmail conversations.
"You can use Gmail's advanced search operators to refine your query. For e.g., the from: operator lets you restrict results to one or more senders, subject: operator restricts results to messages that've your keywords in the subject line, label: operator finds messages with certain label. You can search for label:chat to visualize your chats, label:buzz to visualize your Buzz messages or label:important for messages classified as important," explains Bill Zeller developer.
Download: Graph Your Inbox