Camera Advice

We've decided to upgrade our security system. We want to phase out our existing IP cameras and put in something with more resolution. There will be about 60 cameras on the LAN. We were thinking about mega-pixel cameras with a good virtual zoom and wide-angel coverage rather than PTZ cameras. With so many cameras we're concerned about bandwidth on the LAN and video quality. We thought gigabit ethernet cameras would be a good idea, as well as H.264 compliance, and we'd like to use POE (802.3at at the switch). Our system is centrally located and uses a Gb LAN. We would really appreciate some advice.