Google Apps integrated apps market place is hell. You mentioned Manymoon as a free app. It´s free as long as you don´t use any "sophisticated" features like reordering todo´s - which is of course something never happening in project management. As Zoho Project, integrated with Google Apps for your domain, it is inefficient to use compared to basecamphq and takes more time to keep up to date than it safes you time running your projects. Well, so why not start with basecamphq in the first place.