- Google Sites for the course site itself. You can limit the "sharing" so that the site is only viewable to those enrolled, and you could make the students either collaborators (authors and editors of the site) or viewers only. You can also enable comments on each page of the site, so it would be possible to have basic interaction with 'view only' students.
- Google Calendar for a course calendar.
- Blogger for student writing/journals. With comments, this also allows for basic peer review. Blogger blogs can be made viewable by members only.
- Google Docs for collaborative efforts: writing, spreadsheets, and presentations. An additional benefit is that you can see who did what using the history functions.
- A Google Group for discussions.
- A Google Docs spreadsheet for a gradebook. (This would have to be private or everyone would know everyone else's grades. You'd probably have to email grade updates, unless you wanted to clone the spreadsheet and make one for each student--that might be reasonable for a very small class.)
- A Google Book textbook? That would really depend on your subject. If you could find something, however, Google now has "My Library" with the option to make a "bookshelf" public. It would also be interesting to use Google Books to search your print textbook, even if you couldn't view the whole thing online. With the new Google Book legal settlement maybe some out of print books will become feasible as textbooks.
- Google Docs will display any PDF file, and limit viewership, so you could do readings easily enough.
- YouTube for video lectures, tutorials, screencasts, etc. Students could do video projects, too. Like pretty much everything else, you can limit viewing on YouTube. And there's Picasa for still images.
- Google Scholar for research. Well, sort of. Scholar can be very frustrating if you don't have access to library subscriptions. Personally, I think I'd probably just use the regular web search and teach some good information evaluation skills, assuming I didn't have library access. Though Scholar does index a lot of repositories with great content.
- Since everyone would need a Google Account for this, everyone would have Gmail. Either a contact list or a Google Group would work for announcements.
- Office hours and appointments can be held in GTalk.
- I think everything is embeddable in a Google Site using either widgets or links. It might be possible to use iGoogle for a "personal learning platform" for each student, too. That's were students collect links, RSS feeds, videos, images, etc.
- As an additional benefit, Google does host some amazing archives, too. Google's Life Magazine Image Archive is astonishing. And Google Video hosts a National Archives video collection. Very suitable to educational use. Google Books has articles, now, too. (I think the date listed on that page is the most recent issue, not the only issue, available.)
What else do we need? (Let's avoid the issues of the advantages of having everything in one place, and whether or not we want Google to have our course content and student records.) In a hypothetical sense, what else do you need to teach a course?
And is anyone game?