I once dreamed a large airliner was crashing into the house across the street - nice and slowmo - and I just stood at the window enjoying the spectacle (nevermind the huge fireball and all...)
oh and speaking of fireballs - this one's even better... I must have been around ten, was totally into volcanoes at the time... so here I was, with a friend of mine, being driven by his mom to a neighbouring town for whatever reason, when right beside the street a volcano erupts... we just watch it for a while, then decide we can't really go where we were going with a volcano in the way, so we turn back. Then we're in my friend's room, playing, when... well... one of the walls starts to melt and lava pours in! Strange thing was, I remember thinking "hang on, that wall is on the opposite side of the house from where the volcano was..." - and then sadly I woke... would have been curious to see how that one went on...