Biology: Imagine a snake eating a kangaroo. What does it look like? Like this. (upsetting image warning)
Astronomy: Imagine the biggest object to be found in the Solar system (since Neptune was discovered in 1846). Imagine that was announced today. Pretty cool huh? (thanks to nwhyte)
ETA - The last link is to a page that has since been edited I think. New Scientist seem to have revised the estimation of that object's size down, to smaller than Pluto. So, not the biggest discovery since 1946, but still quite cool.