I tweezed my eyebrows to bits when I was in high school, thinking it would look fantastic to have super-skinny, barely-there brows. Not so. I thought they would grow back, but they did not.
I read that you could use Rogaine to regrow eyebrows (recommended to cancer patients after chemotherapy), so I tried it. Yes, it was expensive, but with the amount you use, a can will last you through tweezing them off and regrowing them about 10 times.
Be careful where you put it - anywhere it touches it will try to enhance hair growth (I used a Q-tip to apply it where my eyebrows used to be).
While I was waiting for them to sprout back up, I used Estee Lauder's Eyebrow Pen/Pencil - you can even buy stencils out there so you don't look like a cartoon drawing when you fill them in.
After about 6 months using Rogaine, my eyebrows grew back, but slightly finer and less bushy then they originally were (no complaints there!). I still fill them in a bit and groom them, but it worked!