As a MS Dynamics CRM developer, what you need first and foremost is CRM Software Development Kit (CRM SDK). 

SDK is a toll Microsoft that has an architectural overview of Microsoft Dynamics CRM, the entity model, security model, web services, and sample code.

CRM SDK contains numerous resources, including code samples designed to help you build powerful vertical applications using the Microsoft Dynamics platform. SDK serves as a guide for developers writing solutions, server-side code, client applications and extensions, custom business logic, plug-ins, integration modules, custom workflow modules and more.

You can down CRM SDK as per the CRM version you are working on from this link. Supporting files, sample codes and tools are available of these links;

Microsoft Dynamics CRM SDK &  MSDN Code Gallery

If you are looking for sample programmes developed without  using Microsoft Visual Studio, follow this link

Some other reliable tools that are used by CRM developers are listed below;

Tools Website/Download Links
Xrm Toolbox Download
Ribbon WorkBench Info and Download
PFE Core Library for 2011 / 2013 / 2015 Download
Dynamics CRM Organization Settings Editor Download
CRM Code Generator for Visual Studio Download
CRM Chart Map Download
XRM Tools Download
CRM Command line Tools Download
CRM 2013 Quick View Menu Download
CRM 2013 Dupe Detection Download
OData Query Designer Download
Trace Reader for Microsoft Dynamics CRM Download
Internet Explorer debugger F12 Details
Custom Code Validation Tool 2013 Download
Custom Code Validation Tool 2015 Download
Legacy Code Checker Tool Download
Sparkle Xrm (CRM 2013 Start Menu navigation) Download
Integration Tools Blog Article
CRM Command Line Tools Download
CRM Early Bound Generator Download
CRM Dev Tools 1.1 Download
CRM Rest Builder Download
MSCRM ToolKit Download
MSXRM Tools Library Download
Diagnostics Tools Download
CRM2011 User Settings Utility Download
Sitemap editor Download
Bulk Workflow Execution Tool Download
CrmXpress Microsoft Dynamics CRM 2011/2013 Download

Please share your experiences regarding the above with me and share any worth mentioning tools that I have missed.