I still need to taste many of the more exaulted wines (e.g. I've never had a red from Niepoort - I'd love to find a $20 Redoma) but from what I've been able to taste, reds only:
Quinta de la Rosa ('07 reserva is VG)
Vallado (wines get more interesting above the basic Douro, but the price soars)
Quinta do Vale D. Maria
Quinta de Macedos (very small, organic, intense wines from the Torto valley)
Crasto (again, once you get above the basic Douro)
Quanta Terra (and the 'lesser' wine, Terra a Terra)
There are also some excellent 'bargain' bottles that pop up from the Douro, like Borges Quinta da Solalheira '07. Hard to imagine a better $11 red....