Google Apps (Advanced Gadgets and Wizards) are a powerful way to add extra functionality to your Google Apps Account. There are also Standard Google Apps Wizards that helps you integrate and embed into Google Sites (eg. Google Checkout Cart).
Many companies have developed for the Google Apps Marketplace , for mainly Business purposes. There are many practical and emerging Google Apps for Education. The Google Apps are All Hosted with Google App Engine, excess bandwidth from increased App traffic can be monitored and modified .
Some Free Google Apps and others have charges ,this does not determine the Quality of the App.
Google Apps for Business is the the largest market in the Google Apps Marketplace . focusing on the connectivity of Google Accounts and business in the Cloud. There are also Google Apps for Education and many other areas.
The Best Google Apps have a 'Wizard' type setup and all Google Account access requests are handled within the Google Apps Wizard.
The following are examples of the Best Google Apps and Google Gadget 'wizards' for Google Sites: