Old question - but I recently needed this along with the row count... here is a query for both - sorted by row count desc:
SELECT t.owner,
t.table_name,
t.num_rows,
Count(*)
FROM all_tables t
LEFT JOIN all_tab_columns c
ON t.table_name = c.table_name
WHERE num_rows IS NOT NULL
GROUP BY t.owner,
t.table_name,
t.num_rows
ORDER BY t.num_rows DESC;