Chrome/Firefox: Notes for Gmail, as the name implies, lets you annotate your emails with great-looking sticky notes. The extension, currently in private beta, packs a lot of useful features, including tags, search and adding notes to any Gmail view.
Once you authorise and install the extension, you'll find a new "Add Note" button in Gmail. Now you can add a note to messages you have to follow up on or are holding onto for future reference. The notes are pinned to the top of the message where you can't miss it.
All of the emails you add notes to are labelled with "Notes" for easy retrieval, but you can also use the regular Gmail search feature to search within your notes. (As of this writing, however, the developers are having an issue with the notes search feature.)
Besides adding notes to individual emails and email threads, you can pin notes just about anywhere. For example, at the top of your sent email label view or starred emails or any other label. If you add an empty label, you can even create a virtual notes corkboard of sorts simply by adding your notes to that label:
There are other ways to add notes to Gmail, but Notes for Gmail has a lot of functionality and a nice interface. The developers are working on adding even more features, but, as it stands, the extension is really handy for adding additional information and details to your email.
A limited number of Lifehacker readers can start using it right now in Chrome or Firefox via the link below: