I always wanted one of those WoW steins. I think that would make a cool present.
As for decorations, maybe some banners or balloons with the Horde sigil on them?
Maybe get a picture of his toon (from wow armory?), blow it up and put it on a big posterboard next to a picture of him. Like a side by side portrait. Hah! "Look who's turning 40!"
Or a toy train, everyone can stand around it going "Chugga chugga CHOO CHOO!"
Edit: Woops didn't see your update when I posted. I'm glad you went with the big portrait idea, I think that will be a hoot.
Edited, Apr 3rd 2012 1:25pm by Pyrenus