if the SO is a she....something from tiffany's is the right choice (in my personal opinion). that's what my family tends to do.
but it doesn't have to be the pen. there are various things there at a multitude of different price levels.
small earrings (ok for hospital wear) or a simple necklace would be nice. rings/bracelets get in the way with all the handwashing, but simple earrings or a necklace would be sweet.
and (as much as i hate to admit this in public) getting a present in that little blue box is special! i've gotten several simple pieces of jewelry to mark special occasions and they mean an aweful lot.
but whatever you decide, i'm sure it'll be well received.