LPs/CDs (probably around 3000, don't know exactly)
Comic books (around 600, mostly FrancoBelgian ones like Tintin, Asterix, Iznogoud, Moebius' comics etc.)
DVDs (it used to be more than 900, but in a first of several steps I recently gave away more than 200 of them to my nephew, my niece and her boyfriend - in the long run I plan to only keep around 300 of the classics like my Laurel & Hardy / Charlie Chaplin / Buster Keaton / Tom & Jerry / Marx Brothers / Thin Man / Alfred Hitchcock / Arthur Penn / Sergio Leone / Francois Truffaut / Billy Wilder / Ernst Lubitsch / Woody Allen / Stanley Kubrick / Cary Grant / Audrey Hepburn etc. movies - the kids wouldn't want those anyway 
I wouldn't call myself a collector though. Music, movies and - to a lesser extent - European comic books are just 3 things I love.
@spurgeonryan: Your step son has good taste. The Smiths were one of the best UK indie bands of the 80s (and the most influential one which explains why they still have new and young fans 24 years after their split).
