Hi there!

I've tried Sanford Vis-a-Vis pen and it works 
fine.  It's an overhead transparency marker, 
permanent extra fine point, and it's non-toxic.  
Right now I'm trying a acrylic artist ink, it's 
pretty much like acrylic paint, but more runny.  
I'm using it in a fountain pen, and there's quite 
a bit of clogging problems.  But it dries on an 
acetate just like acrylic, and the lines are 
thinner than the Vis-a-Vis pen.  Um... that's 
about it, hope this helps.  ^^

-ix