70% cacao content is somewhere around the lowest level of tolerability for chocolate, unless adulterated with some appropriate kind of flavouring (ginger, Earl Grey tea, pepper, for example), although I accept Tomdogggg's point that this is not per se a measure of manufacturing quality. To date, the best we've managed to find is the 88% cacao stuff from Dolfin, who are located somewhere on the southern fringes of Brussels (http://www.dolfin.be we think if you are slavering already) who also perform the above adulterations. Valrhona ain't bad either, though, even though it's French.
Update: Lindt, bless their souls, produce a 99% chocolate. This is an interesting experience, best taken in very small quantities in tasting session conditions; I suspect that even the most devout addicts would be hard pushed to knock it back in any quantity. It certainly sorts out the serious chocaholics from those who are just trying to make their sugar cravings look chic ...
Chocolate and its composition was the subject of a long-running dispute inside the European Union when single market conditions were imposed, albeit not regarding the cacao content per se. A number of countries including France and Belgium refused to accept chocolate which used other fats than cocoa butter, with some backing from the cocoa-producing ACP countries; the British, Irish and Scandinavians had however a tradition of low-quality industrial chocolate production which used palm oil and other vegetable fats in addition to cocoa butter. This led to a certain amount of misinformation from the usual sources with suggestions that Brussels would make the British call their cheap greasy stuff "vegelate" instead of chocolate. In fact, the sole restriction was that such stuff should be labelled with translations of "household milk chocolate" for export to other parts of Europe; no special labelling was required for domestic consumption.