If you are looking for the very best (or at least the most expensive), then you must visit Delud Luxury Blog. For example, the truffle you see in the photo is the Knipschildt’s “La Madeline au Truffe” with a price of $250 for a dark chocolate.
Me, I’ll be happy to eat the wonderful truffles at Simone Marie Belgian Chocolate here in Toronto. 🙂
Smart People I Know 
and here’s more places to go for expensive chocolate!
http://www.trifter.com/Practical-Travel/World-Cuisine/The-Five-Most-Expensive-Chocolates-in-the-World-.45474