How To Create SharePoint 2010 custom visual webpart properties

http://onlinecoder.blogspot.in/2011/04/custom-properties-in-sharepoint-2010_7158.html

https://www.nothingbutsharepoint.com/sites/devwiki/articles/Pages/How-To-Create-SharePoint-2010-custom-visual-webpart-properties.aspx

http://msdn.microsoft.com/en-us/library/dd584174%28v=office.11%29.aspx