What's eating my space ?

Hi,
I wander what is taking up my space on disk ...

btv=# SELECT pg_size_pretty(pg_database_size('btv_good'));
pg_size_pretty
----------------
10 GB
(1 row)

btv=# SELECT nspname || '.' || relname AS "relation",
pg_size_pretty(pg_total_relation_size(C.oid)) AS "total_size"
FROM pg_class C
LEFT JOIN pg_namespace N ON (N.oid = C.relnamespace)
WHERE nspname NOT IN ('pg_catalog', 'information_schema')
AND C.relkind <> 'i'
AND nspname !~ '^pg_toast'
ORDER BY pg_total_relation_size(C.oid) DESC
LIMIT 15;
relation | total_size
--------------------------------------+------------
users.users | 703 MB
btv.material | 557 MB
btv_admin.material | 269 MB
btv_admin.block | 24 MB
btv.block | 20 MB
btv_admin.block_list | 9136 kB
btv.block_list | 9112 kB
multimedia.rel_image_collection2size | 2984 kB
multimedia.rel_image_collection2tag | 1024 kB
btv_admin.block_common | 976 kB
multimedia.image_collection | 936 kB
btv.block_common | 832 kB
users_admin.invalidate_notify | 752 kB
btv_admin.tv_program | 656 kB
btv.rel_material2tag | 592 kB
(15 rows)

The sum of biggest tables is not even close to the total db size .
Some index going wild ?