I attended (part) of Microsoft CRM 4.0 Customization course this week and this are useful links that I collected along the way. They seem to be a small collection of resources for people starting in CRM 4.0 (like myself).
Documentation
Microsoft Dynamics CRM 4.0 Implementation Guide
http://www.microsoft.com/downloads/details.aspx?familyid=1CEB5E01-DE9F-48C0-8CE2-51633EBF4714&displaylang=en
Developer Ramp up Kit for Microsoft Dynamics CRM 4.0
http://msdn.microsoft.com/en-us/library/cc720132.aspx
Welcome to the Microsoft Dynamics CRM Wiki
http://channel9.msdn.com/Wiki/DynamicsCRM/HomePage/
Offline and Online Synchronization in Microsoft Dynamics CRM
http://www.microsoft.com/downloads/details.aspx?FamilyID=c14ca8de-a452-4c9e-b4c9-1c0a51974528&displaylang=en
Books
Working with CRM Second Edition
http://www.amazon.com/gp/product/0735623783
CRM as a Rapid Development Platform
http://www.thecrmbook.com/
Free Add-ons
Microsoft Dynamics CRM 4.0 Software Development Kit (SDK)
http://www.microsoft.com/downloads/details.aspx?FamilyID=82E632A7-FAF9-41E0-8EC1-A2662AAE9DFB&displaylang=en
Online Directory of Microsoft Dynamics Add-on Products
http://www.microsoftdynamicsaddons.com/mscrm-dynamicscrm.html
Accelerators for Microsoft Dynamics CRM
http://www.codeplex.com/crmaccelerators
LINQtoCRM
http://www.codeplex.com/LINQtoCRM
Filtered Lookup for Microsoft Dynamics CRM 4.0
http://www.stunnware.com/
CRM Customization Version Add-In
http://code.msdn.microsoft.com/crmversion
Microsoft CRM Documentation Generator
http://www.codeplex.com/CRMDocumentation
Translation assistant for Microsoft Dynamics CRM 4.0
http://www.patrickverbeeten.com/pages/TechnicalNet/MicrosoftCrm/CrmTranslationAssistant.aspx?id=25
Non-Free Add-ons
Scribe solutions for Microsoft Dynamics CRM
http://scribesoft.com
SalesCentric Custom Views for Microsoft Dynamics CRM
http://salescentric.com
CWR Mobile CRM 4.0
http://cwrmobility.com
c360 (currently down!)
http://c360.com
Blogs and Blog posts
Microsoft Dynamics CRM Team Blog
http://blogs.msdn.com/crm
Highlight: Available downloads for Microsoft Dynamics CRM
http://blogs.msdn.com/crm/archive/2008/11/05/available-downloads-for-microsoft-dynamics-crm.aspx
Microsoft Dynamics CRM Plug-in Template for Visual Studio
http://blogs.msdn.com/crm/archive/2008/10/27/microsoft-dynamics-crm-plug-in-template-for-visual-studio.aspx
Are You Certifiable?
http://blogs.msdn.com/crm/archive/2008/07/23/are-you-certifiable.aspx
Ronald Lemmen - CRM, C# and Cme
http://ronaldlemmen.blogspot.com
Vertical Templates for Microsoft Dynamics CRM
http://www.codeplex.com/crmverticaltemplates