Powering IP cameras

I'd like to install some IP video cameras for my front door, side, and back yard area. I will be running ethernet cables in the attic and then outside of the house to where I want to mount the IP video cameras. I was wondering about powering these cameras. What do I do about power? I only have one electrical outlet in the attic and the HVAC unit is using one of the two plug-in holes. And also, that outlet is prett far away from the IP cameras. What do I do about supplying power to these IP cameras?