I recently bought the Benefit Brow Microfilling Pen and am liking it so far. I also love their Gimme Brow tinted gel like @newgirlnic.
I get my brows tinted and waxed every 6-8 weeks (for free, thanks to a sister who is an esthetician), but I still have little bald-ish spots at the top of both brows that need some filling in.