It was set to GD2 all along, and just stopped working. I tried ImageMagick later, and that didn't work, either, so switched back. The host and I are both at a loss, though I think it's something on the host's side.
if it worked before the move, it's definitely something in the new server; did you try having them use a different version of imagemagick? is gd compiled with FreeType support?