Is there a SFDC tool to quickly load - and reload - test data?

There is Test.loadData(sObjectToken, resourceName) which can be used to load a number of testing records from a CSV file stored as a static resource.

This is great if the intention of the data is for running automated test cases. Not so useful if you want to setup an org for an actual user.

If you're look to copy data into a Sandbox from Production (or another Sandbox) and then do something stuff and then delete the data, then reload etc, you could use the SFXOrgData app (http://www.sfApex.com) which let you copy data and also delete data from your target org.