I've become a fan of Noodler's Heart of Darkness. This ink is blacker than black.
Noodler's Heart of Darkness is one of their bulletproof inks. It flows fantastically, dries quick and doesn't smear. It also doesn't come off anything you get it on, so be prepared. It is permanent. The package also comes with a free rollerball/fountain pen that I haven't bothered with.
I've long been a Parker Quink user, but Heart of Darkness is a much more pleasing black. HoD flows and is absorbed by decent paper in almost exactly the same away as Quink, but it is so much more black. I'm currently using it in my Parker Duofold and my Parker 51, the lines they put down, using Heart of Darkness, is far more consistent than the Quink, and I loved the Quink.
If you want a permanent black ink that'll ensure checks are not forged, and that your writing is never changed, try Noodler's Heart of Darkness.
Noodlers Ink 4.5Oz Heart Of Darkness W/Pen via Amazon