I recently got interested in VoIP (Voice over IP, or IP Telphony), and started writing my own Wiki site filled with interesting stuff I found out about VoIP, but then I found a public Wiki doing exactly the same thing, at www.voip-info.org, and it was so complete, it really put the brakes on my own little project :-). I've not abandonded my Wiki yet, and will probably just refocus it on the subset of VoIP more related to my specific interests and geography. At some point I will even advertise it to others, but for now, take a look at the public site I've mentioned above if you're interested in VoIP.
And if you're not interested, you soon will be. I've not spent any time in this post clarifying what I meant by the title, but the truth is VoIP has really become a hot topic recently, and is rolling out all over the world, already has millions of customers, and thousands of small start-ups are hoping to cash-in on the ride. I expect it will be something like the internet ride in the last decade, albeit a bit smaller. Many fortunes will be made, and many more broken.