Cabernet Sauvignon is often blended with other varieties, most commonly Merlot, as in the Bordeaux blend. Merlot is the most common partner as it adds mid-palate and softness. The traditional Bordeaux blend is made up in varying proportions of Cabernet Sauvignon, Merlot, with smaller amounts of Cabernet Franc, Malbec, and Petit Verdot.
In Australia the classic Cabernet Sauvignon blend is actually with Shiraz, even Penfolds Grange has a little Cabernet. The fruitiness of Shiraz marries well with the structure and acid of Cabernet.