BibMe
I was wondering when someone would finally apply best-of-breed contemporary web design approaches to the realm of citations. Well, BibMe does just that: AJAX and Ruby on Rails underpinnings and a gorgeous interface. What more could a time-strapped undergraduate want?
There are lessons here for applications aimed at more professional scholarly users. Consider how clean and simple it is to enter a book. The default interface allows you to enter a title or isbn:

So I enter my book title, and some AJAX magic quickly brings up a results-list without loading a new page:

Finally, I choose the correct item, and it gives me the pre-filled metadata:

If that auto-fill stuff doesn’t work, a quick JS-enabled flip to the “manual” form yields this:

Nice; this is how all online bibliographic managers ought to work!
My only real critique (and it is fairly minor) is that they didn’t OpenID-enable the service.
And looking farther out, it’s really unfortunate that we’re faced with two levels of application: the simple more-or-less manual citation process of BibMe and others, and the more robust and automated integration of Endnote, Zotero, BookEnds, etc. As word-processors like Word, OpenOffice, Google Docs, etc. and their fil formats (OOXML, ODF) start to get real citation support, though, this awkwardness ought to go away, and we can have richer, more automated and more interoperable solutions.
Note: BibMe prefills “2005″ as the year for my book. While strictly true that it was published in 2005, the copyright date is actually 2006. I think this would result in a technically incorrect bibliographic entry, then (though have seen others cite it this way, so who knows?).
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