The long awaited Business Connectivity Services has entered our Office 365 E3 (and E4) tenants.
Business Connectivity Services bridges the gap between SharePoint sites and other web services, databases, and external business applications. It enables SharePoint to create read and write connections to external data in lists, and to display external information in Web Parts. Imagine being able to consume and update e.g ERP data from within SharePoint Online.
It represents a very important option for you to explore and benefit from.
[NOTE: BCS within SharePoint Online does not support a direct connection to SQL Azure. A WCF endpoint is required. See this blog for guidance]