One of the many great features in Microsoft Dynamics CRM is the ability to customize your implementation for your company's needs. Building the extensibility story into CRM is something that starts from the ground level on day one of the planning of a project. It's a huge cost to the development team but can offer the customer a much better experience because there is no one product that meets all the needs of the diverse business world.
There are three places that I always go to when looking for code to customize Microsoft Dynamics CRM. This assumes that a search of the Internet for a specific solution yields nothing immediately usable. My top three locations for finding code are:
The CRM SDK should be the developers choice for coming up to speed. It will orient the new user to concepts and guidance necessary to create custom solutions for CRM. And it is full of samples, examples, and code.
CodePlex is where complex solutions are placed. It is an open source collection of solutions that can be modified to help create a solution for your company.
The Code Gallery has a lower barrier to entry and contains sample applications, code snippets, and other resources to help the developer community.
Finally I'd be remiss if I didn't mention that blogs have become a real resource for developers who are looking for customization solutions. There are a lot of code examples on the CRM Team blog for example. You can use the Customization or Extensibility and Programmability tags in the left-hand frame to locate a sample of the code available on this blog.