My mind's default songs are 'Smells Like Teen Spirit' by Nirvana, 'One-Winged Angel' - The AC version, or 'She's Like Heroine' by System Of A Down. What's embarrassing is, I usually end up humming/singing along, and playing my air guitar as well. o^_^o

It kinda depends what I've been listening to as well. Last night, I had that Romanian band O-Zone's song stuck in my head. That was hella annoying.