I can offer medium and high-value classic stamps, covers (which is the technical term for letters with stamps on them) and philatelic collections against Bitcoins (although I would accept Primecoins (XPM) as well). I shall not list any specific item for sale in this post, however I am going to try to give you a general idea about the products and services I can offer, as well as the advantages of high-value philatelic items as an investment.
I am a full-time professional philatelist (i.e. expert and consultant) and stamp dealer, having been in the business for more than 8 years already (based in Germany). In the meantime, I have become one of the most active and well-known stamp dealers in the world (philately isn't a gigantic world - however it's growing very quickly), and my reputation in the "real world" can easily be checked upon. I specialise in classic philately, with an emphasis on rare items. I currently serve as advisor to some of the greatest collectors of the moment and I rely on extremely solid technical knowledge, as well as a profound understanding of the market and a vast network of connections in the business, and thus I can advise on either collection-building at the highest level (i.e. for exhibition or simply for personal enjoyment) or buying stamps as a potential investment, or finally simply buying stamps just for the fun of it. Whatever the case, there is nobody else offering top philatelic items against Bitcoins. Amongst all other collectables, stamps tend to be the most valuable in respect to their actual size (there are many stamps and philatelic items which fetch huge prices on the market - yet they are still just very small bits of paper) and the industry is growing at a very fast yet very solid, sustainable pace. And it has done so for the past 20-30 years.
Also, there is another point I would like to make, which is: it is not uncommon in most parts of Europe, the US and probably in some other parts of the world as well, that many households own some sort of stamp collection, usually inherited from the grandparents, built-up over the years, assembled by a child years ago, etc. In almost all of these cases, such collections are virtually worthless. HOWEVER, on the other hand, some of these collections are easily worth tens, hundreds of thousands, or ever one or more millions (of whatever currency). The sale of such property at auction is not taxable in many parts of the world (provided that the same "lucky owner" doesn't come up with a 1M stamp collection every year...). Should one decide to sell his grandfather's collection, or indeed even the collection one has assembled for the past decades, at auction and should it turn out to be worth a lot of money, well, good for him...
I travel extensively across Europe, meeting up with clients, business partners, attending auctions and sourcing fine philatelic properties for sale. Therefore, chances are that I would be easily able to meet up with any serious potential client from most parts of Europe, and any transaction could be completed in person. As far as clients from any other parts of the world are concerned, secure and insured shipping is certainly not a problem, considering my international clientele, and I am ever so happy to escrow, provided that we can find a secure and reliable escrow service with which we both agree.
The reason why I am not listing any specific items here is because I would prefer to first see whether there is any interest for philatelic items within the Bitcoin community, and then work out what sort of things any potential buyer would be interested in (i.e. only collections or only single items or both, any particular country or area (or worldwide), buying as an investor looking to sell the portfolio at auction in the near/mid-term future, or just building up a great collection for fun, etc.), so that I could offer the suitable items to the right clients. Anyway, as a general rule of thumb, I try not to deal in items which are cheaper than EUR 500 per item (whatever the item is - single stamp, collection, etc.), and thus items priced from approx. 1 BTC upwards (at the current rate) is what I can offer.
I shall be looking forward to hearing from anyone interested, and we'll take it from there. Answers here or via PM - I'm sure the Prime-Minister will let me know...