First, I need to take one company out of the running - Iotum. I have interests there that conflict with a completely impartial analysis. Let's just say that Iotum is really rocking, and I completely agree with the always intelligent Jon Arnold.
So, Iotum aside, here's my top three places:
1) Xelor Software : Xelor makes software that works directly with your existing Cisco infrastucture to automatically configure it to live up to VoIP standards. An excellent management team, with Mark Reid from PictureTel, Steven Guthrie from PingTel and Rob Scott from a host of excellent plces.
From their site : Xelor Software provides the first proactive solution to address the three major challenges facing enterprises with IP telephony: the reliability of phone service, the performance of the converged network, and the quality of each call.
The company’s software has been in development for more than three years. The core research and development was undertaken at the Australian Telecommunications Cooperative Research Centre (ATcrc) in Perth, Western Australia. Leveraging years of experience focusing on QoS issues for ATM networks, the initial engineering team applied the maturing standards for Class of Service for Layer 2 networks and Differentiated Service for Layer 3 networks to the fast-growing convergence of voice and data on a single network.
2) Inveneo.org : Only an altruistic geek could come up with this one... it's a wonderful thing to see. Inveneo is a non-profit company that creates products to be placed in ultra-remote places that enable communications infrastructure. I saw their solution that takes a bicycle, attaches a generator to it, then uses it to power a VoIP system. Now, who does that remind you of?
From their site: A low cost, ruggedized, pedal and solar-powered PC and communications system that provides remote villages access to simple computing, voice calling, e-mail and the Internet.
3) SiVox : The company I mentioned that did the call agent training software. It was really, very cool.