Some others come close (like royal, cinnamon and interrupted) but ostrich is the tallest that I have seen. Found a patch the other day by the side of a stream that were at least 6 feet tall.

Depends on site thou I think. Wet acidic site combined with some sun for those ferns to grow tall. Royal Fern reportedly can get quite tall, if you want a challenge.

Dixie Woodland Fern (Dryopteris) seems like the easiest fern to grow tall. I have fronds standing 42" tall on the north side of the house, and they last all summer til winter weather knocks them down, still green.

Thanks everyone!