Normally I wouldn't recommend just a single song, but this song is...for lack of better words...money. Some of my favorite Ratatat songs are the ones that are remixed with existing songs, and I think "We Share our Mother's Health" is an awesome display of just how full and complex Ratatat can make a song.
Basically, if you like Swedish group The Knife and you like Ratatat, you should download this song.