Well the Noisebox EP is the rarest thing I can think of - limited to 150 copies.
Some of the older EPs such as the Any Day Now EP might be quite limited though I think there's a few on Amazon.
The Definitive Vinyl Boxset was limited to just 2000, though I certainly wouldn't sell mine given it's my prized possession (even though I've lost the memory stick!).
Good luck - I hope you find what you're looking for