Google Docs Spreadsheets & Forms

In Google Sites you can embed a form from Google Docs.
Use Google Docs and create a form, then embed it in your Google site by selecting 'Insert' in your Google site page.

Form Example:

This Map is generated using local business center known as Google Places.

Email results of Google Docs Form:

Open the Google form (Spreadsheet/Result View) > Tools > Notification Rules

JavaScript API libraries available for Google Sites
* Google Sites jQuery and jQuery UI >>

Update: jQuery AJAX Form Example