The wife was a 'dead-head' at one point, listening to Grateful Dead etc throughout college days. Alongside that she got into classic rock - Floyd, Zeppelin, Cream (mine), and Sabbath records courtesy of older brother. Of course, she was familiar with some mainstream metal: Metallica, Megadeth (we have two copies of Cryptic Writings in our house, awww), White Zombie.
Then on my side, I came into the equation with more underground metal, depressive English pop-rock (Stone Roses, Smiths, Radiohead, Verve) etc, and the obligatory 70's Swedish porn soundtrack that every marriage needs to survive.
Bands that we both like equally: early Sepultura (her fave by far, she even has a beanie), Mercyful Fate, Radiohead, Black Sabbath, folk stuff like Empyrium, Forseti, and Tenhi, Falkenbach (especially the last one), and Blur.
For a while, our CDs were stacked together. But now I took out all my metal shit and gave them their own rack.
Yeah, sharing a love for music is vital, but it doesn't need to be identical. I've never understood people that aren't into any specific music and just live life by flicking through an FM radio.