Some links to (Early) Christmas (Sheet) Music

Resonet in Laudibus (Jacob Handl / Jacob Gallus arr.)
http://www1.cpdl.org/wiki/images/sheet/handl/gall-re2.pdf

Riu, Riu, Chiu:
http://www2.cpdl.org/wiki/images/1/10/Anonymous-Riu_Riu_Chiu-Uppsala_41.pdf

Psallite, Unigenito:
http://www2.cpdl.org/wiki/images/sheet/pra-psal.pdf

Boar's Head Carol:
http://sca.uwaterloo.ca/Hendricks/Christmas/boarshed.pdf

Coventry Carol:
http://sca.uwaterloo.ca/Hendricks/Christmas/coventry.pdf

Es is Ein Ros Entsprungen:
http://www1.cpdl.org/wiki/images/a/ad/Praetorius-Es_ist_ein_Ros.pdf

A link to parts for "Es ist ein Schnee Gefallen" that is a) Free and b) NOT an arrangement for brass (2 pages).    
http://musicaviva.com/sheetmusic/score.html?vivaid=othm-es-ist     
http://musicaviva.com/sheetmusic/score.html?vivaid=othm-es-ist&no=2
Lyrics for other verses here  http://www.golyr.de/volkslieder/songtext-es-ist-ein-schnee-gefallen-575821.html

Music for "Ecce Mundi Gaudium" here (you have to scroll down for it):
http://www.schelmish.de/site/notendiverse.html#8
Lyrics here:
http://lyrics.doheth.co.uk/songs/mediaeval-baebes/mistletoe-and-wine-a-seasonal-collection/ecce-mundi-gaudium.php

Link to Lochac's "Baroness Cecilia's Essential SCA Songbook", which has "Gaudete" and "Bring Us In Good Ale" among other popular year-round ditties:
http://ildhafn.lochac.sca.org/sites/ildhafn.lochac.sca.org/files/file/music/ceciliassongbook.pdf
(Thanks to sarahbyrdd for pointing us towards this one--Aelinor / Piglet is still using the first (not "after midnight") half, and has added ("Ostgardr Favorites") to it and printed out new booklets  8)

Veni, Veni Emanuel  (four verses):
http://romaaeterna.jp/f200/basil/sb005.html
More lyrics Here:
http://www.fisheaters.com/hymns.html#veniveniemmanuel

Lyrics for "Orientis Partibus":
http://www.tapiasgold.com/december_rains/lyrics/orientis_partibus.html

Personent Hodie:
http://www.8notes.com/scores/11615.asp