gcount is a great app. its not pop but it only uses like 500k of ram and lets you know when you have new mail.
I wanted to add that you can set gcount as your default mail app and then when you click on any email link in any app it will open your default browser to your gmail compose. its a very simple but very handy little app to have and the best part is its free. not a big fan of the mail app myself.