Rolls-Royce Lego Trent 1000:
That's right, a jet engine built entirely of Lego. If memory serves, it's half size, with full interior detail. On display this week at the Farnborough air show.
Not something I'm involved in, but a friend of mine has been working on it quite heavily (leaving the rest of us to pick up the slack with the real work - grumble grumble...)
Also, see here: http://legotrent1000.com/.
There - advertising done