Oh yeah! For example a Bordeaux blend is predominantly Cab, Merlot, and Cab Franc, while a Rhone blend could be Grenache, Mourvedre, and maybe a little Syrah. I don't know if I'd try a Riesling with a Zin...unless you're looking for something that's really tannic with the mouthfeel of raspberry jam and smells like grapefruit...hmm...could be fun?? A great Zin blend is 90% Zin and 10% Petit Sirah if you've got some kicking around. If you want to blend the Riesling...especially if it's sweet....maybe a dry Sauv Blanc to offset some of the sweetness?
But you really can't go wrong with a Cab/Merlot blend!