I have a few. I think they started breeding after I purchased my second machine...
Asteroids Deluxe
Battlezone
Centipede
Mario Bros (narrow body conversion, power supply just went out)
NeoGeo MVS (4-slot with a small stack of carts and a multi-cart)
Omega Race (board died a while back, need to poke and prod it again)
Space Invaders Deluxe
Star Wars
Tempest (monitor died in it a few months ago)
X-Men (4-player)
I also have a few project machines:
Galaga (needs a monitor and control panel)
Multi-CPS2 (currently putting a cap kit on the monitor, houses Marvel Super Heroes, X-Men Children of the Atom and X-Men vs Street Fighter)
Multi fighter (needs a new monitor, houses Soul Calibur, Street Fighter II and Tekken 2)
Nintendo Sheriff cocktail (won't power on)
Omega Race (a second one with board issues)
Stern Meteor pinball
Just enough to keep me out of trouble (or in trouble, depending on who you ask ).