CheckGmail is a nice GMail checker. It blends in the panel because the current version has transparent icons, and it's a nice thing to have, if you're in my place and you uninstalled all e-mail clients because you wanted the browser version and not another software installed on your computer. On a new e-mail, the icon looks like this..
Bad part is that it won't work only with "apt-get install checkgmail". After installing, you'll have to get the latest SVN version with "sudo checkgmail --update". When asked, press capital "Y". That's all folks!