This question has been asked before, please see this: https://stackoverflow.com/questions/12205714/list-of-tables-to-safely-truncate-in-magento
This should help you.
EDIT: For posterity sake:
When you log an issue with Magento support and they ask you to provide a database dump, the script they give you dumps the schema only for the following tables:
If Magento support doesn't need the contents of these tables to resolve issues, it would be a safe assumption that they can be safely truncated.
The catalog_product_flat_* tables and catalog_category_flat_* tables can also be truncated as a reindex will re-populate them.
A user can add entries to the core_url_rewrite table manually from the back end and I wouldn't like to guarantee that two products pr categories with identical URL keys will always have the same URLs after truncating core_url_rewrite. It's not one I'd rely on being able to truncate safely.
Source - Jim OHalloran