Merck's patent on finasteride (for the treatment of BPH) expired on June 19, 2006. Merck was awarded a separate patent for the use of finasteride to treat male pattern baldness. This patent is set to expire in November 2013.
Several companies outside the US currently manufacture generic finasteride, these include; Finpecia, Finast etc. All these generic versions are the same as Propecia, but cheaper. That's just economics. They all contain 1mg Finasteride. Then there's Proscar (5mg Finasteride) and it's generic versions such as Fincar. This is possibly the cheapest source of Finasteride available, many users split the pills into 1mg pieces(5) which would be the equivilant to a Propecia pill. Anyways all the generics are exactly the same as the brand versions, it makes absolutely no sense to not use the generics. Trust me they work, I've used Finpecia and Fincar and had sides with both.