There're a lot of resources online talking about ADO.NET:
1. Data Access and Storage Developer Center: official Data website at microsoft.com.
2. Data Access Blog: team's blog site. You may find information interesting from different team members.
3. .NET Framework Data Access and Storage - MSDN Forums: it's a place where lots of developers are asking questions about ADO.NET and System.Data namespace. Some team mates (including me) are answering questions there. It's good to get feedback from our customers (developers) and help them. However, please do read the FAQ and announcements before posting a question.
4. Channel 9: MSDN channel 9 on ADO.NET. You might find some interesting videos there.
5. Search engine is always helpful:)