I actually liked @Juan's idea for using typesetting pieces to spell "Not Found". Being keen on 3D art, here's a quick mockup I put together just now:
Please excuse the shoddy appearance, I wanted just to give an idea. The final thing will be rendered photorealistically, so all the usual stuff like materials, textures, reflections, etc. will be in place. Also, no problem to use any typeface (that I have installed), or comes as OTF, TrueType or what have you. I think something serif-y would look great, with different typeface for each letter (combining thin and thick letters of different sizes, etc. For added appearance, the typeface bits could be of different "materials", and discernible difference in height, so that it's obvious they come from different typographical sets.
I'm expecting comments, suggestions and critiques, and if enough people think this is a good idea, I'll proceed and create something more finished.
P.S. For the curious, the software is SolidWorks 2009 (no affiliation).
Update: If this gets into double-digit upvotes, I promise a new draft rendered in full glory until Monday.
Now I notice that the letters are actually in the wrong order. Oh well.
Update 2. Here's a second (rendered) version. Quite bland at the moment, I need some extra textures for the floor, I'm thinking of something paper-like, non-reflective, maybe with the printed output of the typography set. The light certainly needs adjustments. The typographic sorts are probably a bit too thick (couldn't find correct measures so I improvised from images). Now, enjoy (or be appalled):
Typeface list upon request. Font suggestions welcome. Comments highly appreciated.
Update 3: Yet another version, with softer tints. But that's not a big deal, those kind of things can be handled with some post-processing, and I'm sure Jin would help with some final touches.