Copy huge Excel data to existing sharepoint custom list

http://3sharp.com/blog/copy-and-paste-from-excel-to-a-sharepoint-list/

You can fetch the records from excel file using .NET code and add them in SharePoint list using SharePoint Server Side Object Model or SharePoint Client Side Object Model. You can easily find the utilities for reading excel files on internet. If you do not find any utility for reading excel files then you can save your excel file in CSV format, read the records, and add them in SharePoint list. You can read CSV file using IO and string operations.