It's fair to say that El Corte Inglés is in a different league to anywhere else. Carrefour (to come) has a far few wines, but nothing like the quality, Mercadona's selection of Valencian wines is frankly pathetic (especially for a Valencian company), while Consum is better. I have a soft spot for the Vidal shops (also to come), for exploring good cheaper wines.
winesofvalencia.com - A personal look at the world of Valencian wine