First of all, I would just like to say that I discovered cult hair care brand Living Proof wayyyyy before Jennifer Aniston did. (She was recently named the face of the brand and is even a stakeholder in the company.) But I'm happy that the brand is getting more exposure, because their products are fantastic.
My favorite is the Restore Mask Treatment. I have to confess that I'm an abuser of hair color. I've been dying and highlighting since college. For all I know, I have an entire head full of grey hair. Right now, however, it is very, very blonde. I'm trying out a bleachy blonde, and have amped up the color significantly. If you've ever bleached you know that your hair can get dangerously straw-like.
I use this mask every other day--leave it on for five minutes in the shower and rinse. The packaging recommends that you use it once a week, but my hair is thirsty. And there's never any kind of heavy residue. Even if you don't bleach your hair unnaturally light shades, winter is not kind to your strands. This mask is a life saver (or rather, a lock saver).