All good answers but I would like to add a few of my views on this.
Papers can be the written piece of work that either supports a presentation at a conference or a written piece of work that gets published in a journal or other academic or professional publication. If the former it often gets written up in the proceedings for the conference and can therefore be referenced in later research / papers by others. This is just the same as a paper in a journal. It does not have to have wide readership as it is down to the later users of the paper to find it (that's called literature review I guess). Obviously there are some journals and conference proceedings that are more prestigious with the resulting increase in weight for the papers / articles contained in them.
Articles, in my opinion, are writings that get published in a journal, professional magazine or even a glossy on your newsagent's shelves. The prestige or weight of the article is down to the author but is typically clear by the journal it is in. If you have published something of a medical nature in a homeopathic magazine it probably (or perhaps should) carry less weight than in say the Lancet or the British Medical Journal.
Reviews are either a comparison of a range of similar items (as seen in hobby magazines, fashion magazines, technology magazines, etc.) or a piece of writing collating or comparing the research in a topic at this time. The latter version is basically someone or some research group's look into the level of knowledge in a topic. This is probably academic in nature and could be published in a journal or in a paper in its own right. It is probably of more weight than the magazine gear review and possibly as much weight as a paper or article in a journal.
In my opinion a blog is an online set of writings, musings and ponderings by someone for their own entertainment or for the benefit of their followers. The weight of the blog depends solely on the weight of the blogger's reputation. If Deming was a blogger he would obviously have a lot more weight in his blog than a lot of people on here being considered a quality guru. However comparing the weight of blogs by a collection of "gurus" in a particular field would basically come down to the opinion of the reader as to which camp they position themselves in. Are you a Crosby, Deming or Juran follower? I reckon it would be interesting if these people had been around in the era of the blogosphere as to whether they would have blogged and whether the blogs would have increased or decreased their reputations.