Here are a few tables that tend to bloat your Magento database. As always, before running any script: MAKE A BACKUP
If you want to save the data, it is easy enough to dump your database and extract the following tables. Over time there tables will grow quite large so it is a good idea to keep them clean!
truncate dataflow_batch_export; truncate dataflow_batch_import; truncate log_customer; truncate log_quote; truncate log_summary; truncate log_summary_type; truncate log_url; truncate log_url_info; truncate log_visitor; truncate log_visitor_info; truncate log_visitor_online; truncate report_viewed_product_index; truncate report_compared_product_index; truncate report_event;
Please comment on any other tables you find useful!
Wait! did I mention ALWAYS MAKE A BACKUP ?