You can empty the _cbsubs_history table. _cm_history and _acymailing_history should also be safe to empty. _cbsubs_notifications you can delete all entries older than a month to be safe. All the _finder tables are Joomlas Smart Search and am unsure what you could safely clear for those. The rest look like you won't be able to clear.

1GB limit is pretty standard for shared hosts. If your site continues to grow you may need to consider upgrading your hosting package, but the above steps should clear out some unnecessary data for the time being.