Altos: The "Las Hormigas" Malbec is a great value and worth seeking out.
Catena: Fabulous Chardonnay, Malbec and Cabernet Sauvignon. Save even more money and buy their Alamos line of wines - terrific values.
Norton: Great Malbec, and the "Privada" cuvee is usually priced very close to my sub-20 target (a definite buy)
Lurton: Good Cabernet, should have a good Malbec as well.
Zuccardi: The Zuccardi "Q" Malbec is a terrific wine, but I have not tried their other offerings.