It is usually blended with other varietals, rather than made a stand-alone wine. In France it is found in many Rhône blends, especially Châteauneuf-du-Pape.
Garnacha is the Spanish name. The grape was grown in Spain before it made its way to France, but the popularity of the French wines has ensured that it is now more commonly known by the French name. It is also known in the Catalan ragion as Garnatxa.
Officially, the Spanish name consists of two varieties: the white Garnacha Blanca (Grenache Blanc) and the more popular red Garnacha Tinta (Grenache Noir).
About 'Garnatxa Blanca' (this is the Catalan spelling for the grape name) whites (specially the ones made in Priorat, Montsant, Tarragona, and Terra Alta), I have to confess I do love and enjoy them very much.
Of course you can find some not very good whites from garnatxa blanca, but I do believe they are in general very good.