According to Ross Garfield, otherwise known as The Drum Doctor, the single most important thing that you can do to make your drums sound great is to install new heads. But which ones? There are so many to choose from, that it's really hard to tell which ones are correct for the type of music that you're playing.
But we're lucky that we're living in the age of instant video, since Gear Guruz posted an excellent video comparing the sound of different snare drum heads. Don't equate the one that sounds better in this video as the best one for you though, since the sound only applies to the particular song, but do listen to the major differences between heads.