For Linq-to-entities you can check MSDN:
- Syntax examples
- Linq-to-entities
Sources for EFv4.1 code first are:
- ADO.NET team blog
- Morteza Manavi's blog
- Julia Lerman's blog
- Stack Overflow
As I know there is no book covering EFv4.1 yet.
Edit (May 2012): There are two books about EFv4.2 (Code first / DbContext API) now:
- Programming EF Code First
- Programming EF DbContext