Oh, I use everything! Laura Mercier (foundation, a few lip products), Bobbi Brown (blushes, gel eyeliners), NARS (blush), Chanel (everything! eyeliner, face products, lip products, eyeshadow, brushes... I adore this line), Fresh (mascara), Lancome (mascara, eyeliner, this is a really good line, too), MAC (some eyeshadows), MUFE (HD powder - it's amazing)
I couldn't stick with just one line, though, because I would get bored. If I had to it would probably be Chanel... well, if I had to and if I won the lottery at the same time.