Like many who have the HF10, HF100 etc, my battery has a pretty short life. So I need to buy a new battery for my camera. I know the Canon one is almost $100, so I was wondering if anyone has tried any third party battery.

Do a search for a "decoded BP827". It's a much bigger battery that will last for several hours, and will correctly report the battery life. Other 3rd party batteries aren't chipped/decoded, and while they work well enough, you don't know how much life is left.

We have two types of BP-827 available.

This is the Bp-827 without the info-chip. You will get a warning everytime you turn on the camera. The LCD screen will not show remaining battery level. however, there is a button and 4 LED indication on the front on the battery that you can check the remaining battery level easily.
BP-827 Canon Compatible Battery with LED Indicator | L.A. Color Shop (http://lacolorshop.com/products/item.asp?id=bp827led)

This is the fully decoded BP-827 that function just like the stock canon battery.. and less than half the price.
Canon BP-827 Fully Decoded Compatible Battery | L.A. Color Shop (http://lacolorshop.com/products/item.asp?id=bp827n)