I would like an account of the historical literature on the Planetary
Conjunction of 1186 (the so-called "Deluge Conjunction"), and the
apocalyptic panic which subsequently spread across Europe.

How do we know about the panic and the Conjunction? Who are the key
primary and secondary sources? How can I find texts of the key
sources? (I am willing to go to the library to find sources if they
are not available online, but would appreciate bibliographic citation.
Texts available at the Bibliotheque Nationale de France are
particularly appreciated.) I am especially interested in finding a
copy of the so-called "Letter of Toledo." Which medieval historians
have written about the Planetary Conjunction? Is there a standard work
on the subject? A work that places the Conjunction within an
astrological context? An apocalyptic context?

Hello medhist-ga

Further to my comment below, I have found the following:

The English text of the Toledo letter online in a collection of text
files relating to a course "Apocalypse, the Millennium, and History "
at  Hamilton College
http://academics.hamilton.edu/religious_studies/rseager/re336.00/text_medieval.html#1
 Unfortunately no source for the text is stated, but the page is by R
Seager, whose details are at
http://onthehill.hamilton.edu/academics/faculty.html?dept=Religious%20Studies

An account of the voyages of Richard 1 in the Holy Land "Richard of
Holy Trinity once ascribed to Geoffrey of Vinsauf)" , which mentions
the conjunction. This is in an online collection of medieval texts at
York University, Ontario
http://www.yorku.ca/inpar/richard_of_holy_trinity.pdf.

an extract from a fairly dismissive comment about the conjunction in
the "Annales Marbacenses." and commentary on the comment in a mailing
list message by Richard Kay, Department of History, University of
Kansas  at http://www.ku.edu/~medieval/melcher/matthias/t104/0099.html
 I have also found that this is from a discussion on Mediev-L:
"Astrology, Millennialism, and Us"  The other threads for this
discussion, which may include references to other source material, can
be found in the archives at
http://www.ku.edu/~medieval/melcher/matthias/t103/
http://www.ku.edu/~medieval/melcher/matthias/t104/
The only reference to any edition of the Annales I can find is
"Annales Marbacenses qui dicuntur." Anhang: Annales Alsatici
breviores.
Edited by Hermann Bloch. 8to. 1907. Reprint 1979. on the site of the
Ancient and Medieval Studies Reading Room at Columbia
http://www.columbia.edu/cu/lweb/indiv/manc/mgh.html

This last item mentions the "Toledo Tables" of astronomical data which
would have been available to astrologers of the time.  Fritz S.
Pedersen of the University of Copenhagen has a project on the Toledo
Tables, and provides some data about the source manuscripts at
http://www.igl.ku.dk/~fsp/

The chronicle of Roger of Hoveden were translated by Henry T. Riley
and published as "The Annals of Roger de Hoveden".  2 vols. London: 
Bohn, 1853.
 "Chronica Magistri Rogeri de Houedene" edited by William Stubbs,
published in 1868 by Longmans, Green, Reader, and Dyer, London is
available at the web site of the Bibliotheque Nationale de France
http://gallica.bnf.fr/ (click on Recherche and use words from the
title in your search).

Gesta Regis Henrici Secundi Benedicti Abbatis. The Chronicle of the
Reigns of Henry II and Richard I. A.D. 1169-1192; by Benedict of
Peterborough, edited, from the Cotton MSS. by William Stubbs (London:
Longmans, Green, Reader, and Dyer: 1867 is also available at
http://gallica.bnf.fr/

A text in Italian by Guido Horn d'Arturo "NUMERI ARABICI E SIMBOLI
CELESTI" which appeared in Pubblicazioni dell'Osservatorio Astronomico
della R. Universitŕ di Bologna", I, 7, 1925 and is reproduced on the
web site of the Observatory of Bologna at
http://www.bo.astro.it/~biblio/Horn/Horn_page/arabi.html discusses the
conjunction (scroll down to Capo III) and gives a list of historical
sources.

Rigord wrote the Gesta Philippi Augusti, dealing with the life of the
French king, Philip Augustus, from his coronation in 1179 until 1206.
It was published in tome xvii. of Dom Bouquet’s Recueil des historiens
des Gaules ci de la France (Paris, 1738—1876); and with introduction
by H. F. Delaborde (Paris, 1882—85). A French translation of the Gesta
is in tome xi. of Guizot’s Collection des mémoires relatifs a
l’histoire de France (Paris, 1825).
(information from http://42.1911encyclopedia.org/R/RI/RILEY_JAMES_WHITCOMB.htm)

A modern commentary on the event expresses disappointment: "Even
though we have not personally delved into detailed chronologies of the
period, we are nonetheless disquieted over the lack of references to
the year 1186 as unusual in any sense.  In the light of the zodiacal
situation, we would suppose that the conjunction had something epochal
to do with the history of Mariolatry, virgin worship, but reference
material along this line is not accessible at the present time."
http://www.magee.demon.co.uk/extracon.txt Sidereal Astrology Home Page


Search strategy: 1. planets, conjunction, 1186  2. "Roger of Hoveden",
3 "Benedict of Peterborough", 4. Rigord, 5. "Annales Marbacenses"

I hope this will provide you with a good start to your research

This was a spectacular guide to the online resources. The only thing I
could have asked for in addition was some guide to the established
literature -- the secondary sources NOT available on-line. But the
response given more than satisfied me.

This might give you a start:
"Roger of Hoveden, Benedict of Peterborough and Rigord in his life of
Philip II together provide us with the texts of four circular letters
concerning a conjunction of all seven planets in the constellation
Libra in September 1186."

The first was from someone called "Corumphiza" who predicted disaster
for the Arabs, the second was by "William, who we are told is the
clerk to the constable of Chester" and who predicts victory of
Christians over pagans, the third "from a monk called Anselm in
Winchester tells of a lay brother there who fell into a trance,
recited some dreadful Latin verse concerning the dreadful things to
happen at the forthcoming conjunction, and promptly expired. ... the
fourth one, claiming to be from 'Pharamella son of Abdullah of
Cordoba, to John, bishop of Toledo'. The writer claims to be a
Moroccan Arab who has come across the first letter, from Corumphiza,
and makes caustic comments about the ability of the Christians to
interpret the stars. His first criticism is that such planetary
conjunctions happen from time to time anyway without great disaster
striking, which is fair enough. His second point is that in any case
the anticipated conjunction will not take place in September 1186:
Mars and Venus will not be in Libra. This is simply untrue, as the
writer would have known if he were a real astrologer."

from Astronomy and Astrology in the 12th century - Nicholas Whyte at
http://www.kepler.edu/articles/astrology/whyte.html

I forgot to search on "deluge conjunction" when compiling my answer.

This search gave me just one reference: “The scholar Bar Hebraeus
wrote of the "all planet conjunction" of 14th September 1186: "..all
the astronomers predicted that a universal flood and a mighty
whirlwind would would take place in the world, and all mankind would
perish."” http://www.calendersign.ric.at/en/topics/turn_of_era1/

Further searches on Bar Hebraeus did not come up with anything
obviously relevant, but did serendipitously uncover the following:
For Michael the Syrian (Micheal the Great) “any apocalyptic
speculation was inconsistent with his repeatedly emphasised belief
that God was almighty, and he told his flock accordingly, when they
were shaken by eschatological fear in 1186” (Michael, chronicle, 731
(III, 399)). From Originality and Function of Formal Structures in the
Chronicle of Michael the Great by Dorothea WELTECKE, HUGOYE: JOURNAL
OF SYRIAC STUDIES, Vol. 3, No. 2, July 2000
http://syrcom.cua.edu/Hugoye/Vol3No2/HV3N2Weltecke.html#FN70