What's your favourite gear ratio?

Hi, I'm currently planning on converting an old road bike to a fix gear bike, but I live by loads of hills so I'm worried that I won't be able to ride it anywhere! Can anyone suggest what sort of gear ratio I should be using?

How about a set up which provides a choice of ratios to suit the terrain? I hear the continentals have gone over to such a system almost completely, and even some English racers are now experimenting with it.