Remember, you can use the comparison and report card spreadsheets for an at-a-glance look at the features, benefits, and drawbacks of each tool. (For your reference, here they are again: Collaborating Report Card and Collaborating Feature Comparison)
Google Docs: Easy to upload files and collaborate in one central location, but not robust enough for building an online community.
Google Groups: Quick and easy to set up, and great for sharing ideas and staying in contact; lacks a file structure for organizing documents.
Google Sites: Quick and easy to set up; great for sharing ideas, staying in contact, and creating an online community. Requires more time and skill to set up than Google Groups.
Zoho Wiki: Very effective for organizing information, but requires a higher level of technical skill.