Assuming you're migrating from the file system:
- Windows Explorer view for simple scenarios (limited feedback if something goes wrong)
- You can try if MS SyncToy supports 2007 (free tool, advanced features)
- There are free community tools out there on TechNet gallery and CodePlex
- Lastly, to do an Enterprise level migration you will need to use a commercial product such as DocAve or Quest
So it depends on your needs and requirements
Kind regards,
Margriet Bruggeman
Lois & Clark IT Services
web site: http://www.loisandclark.eu
blog: http://www.sharepointdragons.com