GMail Sidebar/Panel is now available.
I have taken the keyboard shortcuts from and reformatted them into two columns, removed superfluous information, and resized the fonts, etc to make it more suitable for use as a sidebar
GMail is a great app, but I only seem to remember some of the keyboard shortcuts. I knew there were more, so I went to look at them — only to see that there is a one since I last checked.
I thought about bookmarking it, but realized that it would make a good sidebar. Please note that I have organized this according to which keyboard shortcuts I do not already know (those are at the bottom, the ones I want to learn are at the top). I have also taken out the explanations of what they do, under the assumption that this will serve as a reminder rather than a learning tool. I have also adjusted the fonts according to my personal preferences.
The good news is that the HTML has been cleaned up so that it should be simple for anyone with even the slightest bit of knowledge to reorganize it to an order of their own liking, and the page now uses CSS so if you want to change the fonts, colors, etc it should now be a simple matter to do so.
Clicking this link (in Opera) will prompt you to add it as a panel GMail Keys OR right-click this link: GMail Sidebar/Panel and save it to your hard drive, and then add it as a panel from there using Opera’s “File > Open…” command.
You can add any page as a sidebar/panel by bookmarking it (Windows Users: press ctrl + d Mac users: press cmd + d) which will bring up this window:

and click the “Details >>” button and check the box next to “Show In Panel” as seen here:

That way you can edit any changes that you want and make this panel your own.
Note #1: “Panel” and “Sidebar” are two ways of referring to the same thing. I tend to prefer “Sidebar” but it appears that Opera is moving towards calling them Panels.
Note #2: My thanks to Google for a) creating GMail, b) creating keyboard shortcuts for it, and c) not suing me for repackaging their information in this format.