GmailerXP - Home: "GmailerXP is the be-all-end-all utility app for Google's Gmail service. The program allows users to do anything that they can do online, it also combines all the features of the other programs (GML, Gmailto, etc.) The ONLY Gmail app you'll ever need."

viksoe.dk - GMail Drive shell extension: "GMail Drive shell extension

GMail Drive is a Shell Namespace Extension that creates a virtual filesystem around your Google GMail account, allowing you to use GMail as a storage medium."