Contact form with Ajax that can be integrated with any website very easily and could be configured in minutes, without modifying any line in the actual source code. Plenty of pre-defined examples help you integrate the script the way you want it, whether database storage, csv export or submission to Google Spreadsheet. You can enable/disable any feature like IP inclusion, auto-responder etc in configuration files. Extending the reForm could be done via available plugin files, extend reform without changing core files!
Download ReForm - The Ajax Contact+ Form