I'm sure there is an app for iPads/iPhones that would enable you to monitor several rooms at once. The only downside there would be the need for 5 devices (4 for each room, one for you). I used our iPad/iPhone combo for a bit. Worked pretty well, but we only had the pair, so I never looked into the possibility of doing multiple rooms.

I finally gave in and bought a Lorex video monitor. They come with up to 4 cameras and a video monitor. You can watch all 4 screens simultaneously (the audio switches between cameras) or it will scan through all the cameras in full screen. It's not cheap though (they had a sale and free shipping when I bought it and it was still $240. I found one for $210 I think, but again, there was a sale and such. So worth it though! Carting around 4 monitors everywhere I went in the house was beyond annoying.