Important web part Urls:

http://mysharepointwork.blogspot.in/2010/05/sharepoint-2010-webpart-tutorial.html

http://msdn.microsoft.com/en-us/library/ff742312.aspx

http://msdn.microsoft.com/en-us/library/ff597538.aspx

http://geekswithblogs.net/juanlarios/archive/2010/10/24/web-part-development-in-

sharepoint-2010---what-you-need.aspx

http://johanolivier.blogspot.in/2010/08/basic-sharepoint-2010-linq-web-part.html