Most of time SharePoint developers implement custom user controls, web parts, application page, in the past i was developing all custom required controls using ASP.Net server controls like button, label , grid , … etc and then apply different CSS and themes to make it looks like SharePoint controls, in SharePoint you have The Microsoft.SharePoint.WebControls namespace of the Microsoft.SharePoint.dll contains a number of SharePoint server controls that you can use in you web parts and application pages. you can use it within SharePoint context. the following link illustrate all available server controls you can use within your custom controls to be looked like SharePoint control and maintain the same theme.
http://msdn.microsoft.com/en-us/library/microsoft.sharepoint.portal.webcontrols.aspx
http://msdn.microsoft.com/en-us/library/microsoft.sharepoint.webcontrols.aspx
also the following link explains some of controls with examples implemented in SharePoint 2010 and it will be the same in SharePoint 2013
