I use PRTG Network Monitor to monitor pretty much everything, and it works very well. I get email alerts when anything critical happens and can also monitor the status of everything from both the windows GUI or the web interface.
I decided to create a map of the office yesterday and then overlay sensors for each machine on top of the image. I have a sensor for each machine which pings it every 30 seconds and keeps a track of its status. I had already created a Visio document of the office layout with the location of each machine and so I simply saved this as a JPG image and then copied it to C:\Program Files (x86)\PRTG Network Monitor\website\images on the PRTG machine. This image was then accessible by going to http://PRTGMachine/images/office.jpg.
Next I created a map from the WebGUI and entered the background image. Once the background image was in, I simply added all the machine sensors and then then placed them over the top of the machine icons on my background image.
Now I can view the status of all the machines in the office on the map and quickly spot if there are problems with any machines and where they are located.
I also created a map for the key network components and their status.