The network monitoring market will be huge as when you install VoIP you also have to ensure your network is tuned for optimal VoIP transmission at all times. You really can’t deploy VoIP on a busy network without also being able to monitor the network effectively. Enter Netcordia and their NetMRI tools. They graphically display the health of your network in a concise and easy to read way. Recently the NetMRI software was upgraded to version 1.5 meaning the software is more flexible and works with ore vendors than ever before.
From an investment standpoint the network monitoring space should be a fantastic area because all networks need this tool. In reality there are about a dozen companies who all think they are leaders in the space yet no one has heard of any of them. Netcordia is one of the better known companies in the space and they do a good job of promoting themselves.
Still by now there should be a clear market leader in this space and a company with real resources could own the market quite rapidly. VCs are you listening?