1. Microsoft’s SQL Azure
3. SalesForce.com’s Database.com
4. Intuit’s QuickBase
7. ZeusDB [Thank you Antonio Burgess for mentioning it in comment thread]
8. Google App Engine Data Store
I’ll keep on updating this list as i stumble upon new databases in the cloud.
Also if you know Cloud DB’s that are not in the list, drop me the name in the comment and i’ll include it with due credit.
Update March 23 2012: Added DynamoDB