izneo.com is a site for French readers. From 1.99 euros you can read hundreds of comics online.
Apparently it's a joint project by some of the leading Franco-Belgian comic publishers to combat piracy. They put HQ scans of their comics online in Flash format; you're entitled to read the first five pages of each book for free and then pay in order to read the whole story, using your credit card or via Paypal.
It includes hundreds of titles, from old and out-of-print to more recent publications.
If you can read French then
bon lecture.