3D Arena (items free first day and go up to regular price in 4 days)
3-darena.com/index.php

RenderCenter Adventskalender
www.render-center.eu/adventskalender/

Bambi‘s Adventskalender 2007
grafikbambi.gr.funpic.de/xmas.htm

Evil Innocence
evilinnocence.com/

RenaPD‘s L33T Christmas Wear Textures
www.renderosity.com/mod/gallery/index.php

CG Realms Xmas 2006
cgrealms.com/Freebies/xmas2006

M3 Santa Outfit 1 Complete outfit with hair and Character
www.3dpmr.org/freestuff/3dpmr/SantaM3/index.htm

Studio Maya - Ball Joint Doll Santa Set and some older Christmas freebies
www.3digitalcrafts.net/studiomaya/1download/index.html

2007 Cinema4D advent calendar
c4dtreff.de/c4dak2007/adventskalender.php
2006 Spanish C4D advent calendar
www.c4des.com/navidad/regalos.htm
2007 French c4D
ns352037.ovh.net/~avent/gdpn/
2005 C4Forum advent calendar
www.c4dforum.de/calendar2005/adventskalender.php4
2005 C4Forum advent calendar
www.c4d-forum.de/adventskalender2004/adventskalender.php4

PoserPros 2006 freebies
poserpros.daz3d.com/forums/viewtopic.php

Neonutters 2003-2006 2D freebies
http://www.neonuttersofneopia.com/advent2003.php

Realm of Savage 2006 freebies
http://www.realmofsavage.com/holiday_dloads.htm

Movie Grinch still at
3d4food.com/free.html

I found a bunch of new links, but to give credit where credit's due, a bunch of the links were found at forumromanum.de

Oddly, while there are a lot of C4D advent calendars, there aren't for any other software program besides Poser.

My visual indexes of Poser content are at http://www.sharecg.com/pf/rgagnon