Wake on LAN

I need to use Wake on LAN to wake-up 300+ computers on my network at a specific time during the night. I need a free or in-expensive program to do this. Or is there any other way to do this.
We use HP and Compaq pc's here and by default they are all set up in the BIOS for WOL I just need some way of waking them up that is cheep or free.

Any suggestions?

Thanks
Clay