There are many website out there to help any developer. This is most of the times obvious question asked by interviewers that which websites you refer when you are stuck.So below is the answer to that question. Most used website or forums used by .NET developers. These websites also provides information about basic to advanced errors, developer queries, resource optimization techniques. Some websites are not directly or indirectly related to all types of developer irrespective of the programming language and technology they work with. Some of the website provide ready to consume package for rapid and error free development. Certain websites provide open source projects/ application which can be extended or modified as per personal desire.
There may be many more. Please share links to more related websites in comments to make the list more exhaustive and useful.