To uninstall an application purchased or otherwise installed from the iPad App Store, simply do the following:
1. Hold your finger on either the icon for the application you wish to uninstall or any other icon until the icons on your home screen begin to shake or wiggle (the same action you take to move or re-arrange home screen icons).
2. Click the "X" in the upper left hand corner of the icon for the application you wish to remove.
3. When prompted, touch Delete.
4. To prevent the app from re-syncing to your iPad, plug the iPad into your computer. Under the iPad -> Applications tab in iTunes, de-select the application from the Sync Applications list.
If you have deleted the app from your computer, and you want to re-install the application at a later time, simply visit the AppStore and select the application again.
Note: if you're experiencing difficulty removing an iPad app that seems to be "stuck" installing (i.e. endlessly "Waiting ..."), read this FAQ on How to Remove / Delete a Stuck iPad App.