Official Microsoft Online Resources

Microsoft Dynamics CRM Dev Centre
http://msdn.microsoft.com/en-us/dynamics/crm/default.aspx

Microsoft Dynamics CRM Forum
http://forums.microsoft.com/dynamics/default.aspx?siteid=27

Application Development in Microsoft Dynamics CRM 4.0
http://msdn.microsoft.com/en-us/library/cc948985.aspx

Dynamics CRM 4.0 Solution Center
http://support.microsoft.com/ph/12976

Microsoft Dynamics CRM 4.0 User's Guide
http://www.microsoft.com/downloads/details.aspx?FamilyId=0DB4D487-1BAA-4619-9BC5-074D73C3997D&displaylang=en