Hmm, A LOT! Well, mostly on Nintendo stuff due to their consoles/handhelds and their awesome games.
I do have some Simpsons merchandises but not as much as my Mario/Nintendo collection. I mostly have Simpsons DVDs, books & comics, some board games, some Burger King toys, three USB flash drives, few shirts & a hat, some cups, and some figurines & plushies.
I do like to collect Lisa & Maggie merchandises though.