Gmail automatically detects commonly emailed links such as Youtube videos, Picasa photo albums and Flickr links, and gives you a preview from within your Gmail Inbox. In order to enable this feature, go to Settings > Labsand enable Inbox preview.
Control incoming mail:
Go to Settings > Filters and set up filters to automatically label, archieve, delete, or forward mail with specified criteria. You can do so based on any message. You can select Filter messages Like this from the “More actions” drop-down menu.
Undo Sent mail:
Go to settings and choose the time delay before an email is actually sent, so that you can cancel sending and edit your message again. This is quite handy, especially when you realise you sent the email to the wrong recipient.
Select multiple messages:
To select multiple messages in your Gmail inbox, just select the first message in the series, hold [Shift] key and then select the last message. After this you can apply ant action, like archiving or adding a label, to this whole set of messages.
Emphasize words in chat:
Unlike other chat clients such as Yahoo! messenger, Gmail doesn’t support text formatting options. However, it does let you add some basic formatting as you type, enabling you to emphasise words from the remainder text. In case you want to make a certain portion of your convertion blod, enclose it within asterisks. For example, type *text*. You can also italicise text. To do this, use underscores instead of asterisks as follows: _text_. Similarly, you can strkethrough your text by enclosing the text within hyphens. For example, type -text-.