This sort of thing is best done in a Wiki. It's so widely applicable, perhaps it should be in Wikipedia, although there'd be a constant battle with the Wikipedia insiders about notability and trusted sources.
But there is a
MobileRead Wiki
And we even have
a page for ebook stores
And it certainly needs updating to eliminate dead stores (e.g. Fictionwise). And highlighting which use DRM might be useful.
Have at it!