I've never been to TED, but wow are the talks there inspiring and insightful. They also cover a wide range of topics far beyond just IT. The majority of the talks are also available online, some in high quality 480 progressive mp4 as well.
The best thing I've always found about going to conferences, is the inspiration that I can get and find in the talks others give. TED inspires in a different way, so here's a few of my favorites and why:
Dr. Dean Ornish: The world now eats (and dies) like Americans Only 3 minutes, WATCH IT. The power of your diet to kill you is rather amazing, if you want an even more comprehensive background on this, read The China Study
Might You Live a Great Deal Longer? A very fascinating theme, which includes several talks, including the short 3 minute one I cited separately in the hopes more people would watch it. :)
Richard Dawkins: An atheist's call to arms This one is sure to get a few people in a huff, for Richard Dawkins has few kind words for those who hold religious beliefs dear to their heart. But its a very interesting talk on science, and oddly enough I didn't find it very scornful (which some do), probably my background in Philosophy.
Blaise Aguera y Arcas: Jaw-dropping Photosynth Demo This one has been posted by people before, I have to include it cause its definitely rather incredible to see. Definitely a tech theme on this one.
And finally, one of the most relevant to our current crises with regards to the environment and sustainability…
Janine Benyus: 12 sustainable design ideas from nature A very exciting talk about work being done to copy sustainable ideas from nature, also called biomimicry. If you're looking for an upper, this one definitely left my with a smile and some hope for future developments that don't require us to devastate places with mining, pollute the environment shipping raw materials around the world, etc.
I'm sure I missed a lot of good videos, if there's something that really inspired or awed you that can be found in the TED talks, please share!