I'm a bit of a space exploration enthusiast myself, so of course I have to list a few TED talks on that as well...
The future of space flight
Exploring Earth and the solar system
I would love to see this happen... This might be my favourite talk of them all. I was almost applauding myself at the end.
This was a really cool project that never happened (for good or bad... atomic rockets are a bit risky but very powerful).
Our place in the cosmos
...and really a lot more than cosmology...
World wide telescope
I wasn't sure if this should be under the heading "Space" or "IT", but here it is...