Patagonia R1 Headband - 2007 BCS

I've been running in it in the cold and it keeps my brow dry enough to prevent ice buildup (which is more than I can say for my neck-gaiter).
I have also used it in the gym, which might be a better comparison to warm weather. It wicks sweat off my face just fine, and washes repeatedly without developing pills or other wear-signs, but it is so warm that I would not recommend it for summer running.
If you are unfamiliar with the Patagonia R1 fleece, then be warned that it IS fleece. It is fairly lightweight and wicks wonderfully, but it's not a sweatband so much as it is a cold-weather headband. If you're thinking about spring and fall running and live in a cold climate, then this is the best thing I've tried. If you're looking for a summer sweatband, look elsewhere.

Update: as to the ponytail question, just had my girlfriend try it on. She says it'd work fine to keep your hair off of your face. Order a size down if that's your priority though. I have a pretty big head and the large is not tight enough on my noggin to keep hair back (or at least I imagine it isn't).

This'll work fine for that.

note that this sizing guide does not give you a "snug" fit. It keeps the headband pretty loose.
I have a big head (I think 9 on the scale used here), and it's still comfortably loose. Stays up, but doesn't hug my ears close to my head.

Put a tape measure around your head. Divide the number of inches by two. 6.5-7 is small, 7-7.5 is medium, 7.5 & above is large.