I’m not usually much of a ink guy, but since I’ve gotten back into using fountain pens there are a few that I’ve tried:
Noodler’s Old Manhattan Black
This is one really, really, black ink. It’s so black it looks strange on the page. It writes well, and is permanent. It doesn’t seem to last well in the pen, because it flows pretty heavy I think.
I tried this one because Richard Binder suggested it on his site, and it’s a pretty well behaved ink. Not really black enough for my taste, however.
Mont Blanc Blue/Black
Some say that using iron gall inks will ruin a pen, but my M200 doesn’t seem any the worse for wear – the ink window didn’t stain at all. The ink lasts pretty well in the pen, but it writes a little scratchier than the other stuff. It’s permanent, and has a nice color.