d20 Modern
There's a whole lot more than just Urban Arcana, Weapons Locker, and Future, seven more specifically, and that's just the official WotC stuff. There is a bunch of stuff from 3rd party publishers for it, especially from the RPG Objects line.
I bought up the whole line of d20 Modern when it was first published, and have picked up the occasional 3rd party pdf since then. While it doesn't stand particularly well on its own, d20 Modern was built with modularity and interconnectivity in mind, and works very well with other d20 products.