Converting video to play on apple tv

Hi, I have ordered an Apple tv 2. So i am wanting to convert the many video files on my PC to mp4 so i can put them in iTunes.

My question is, can anyone recommend a good (fast if poss) program to do the converting.

I have spent ages on google trying to find somthing, but there is quite frankly a lot of crap there and i dont have time go through it all.

Surely some of you good people can point me in the right direction.

Thanks

Ross.