The SharePoint 2007 Test Data Population Tool(SPTDataPop) is available as a command-line executable utility which generates test data in a jiffy. This tool might be useful for performance and load testing for your project.
The SharePoint Content Deployment Wizard from Chris Obrien is a excellent tool for SharePoint 2007 content deployment.
There are situations when we want to create empty site collection, like when your content deployment job is failing due to conflicting content. In these cases STSADM.EXE comes handy.
STSADM.EXE is the only means to create a completely empty site collection.
Here are some really useful SharePoint tools available at CodePlex. I have tried some of these tools while others in the list seems to be popular and worth checking.
CodePlex is Microsoft’s open source project hosting web site.