Sites: Customization

[BladeRunner]

Windows:

High Definition Wallpapers: http://www.hdwallpapers.net/
InterfaceLIFT: http://interfacelift.com/wallpaper_beta/.../date/any/
Good-Walls: http://www.good-walls.com/
ProWallpapers: http://www.prowallpapers.com/index
Vladstudio: http://www.vladstudio.com/home/
WinMatrix: http://www.winmatrix.com/
WinCostumize: http://www.wincustomize.com/
VistaStyles: http://vistastyles.org/
devianART: http://www.deviantart.com/
ThemeXP: http://www.themexp.org/
StudioTwentyEight: http://www.studiotwentyeight.com/
2Desktop: http://www.2desktop.com/
adni18: http://www.adni18.com/index.html
MyVistaThemes: http://www.myvistathemes.com/
5X: http://www.x-x-x-x-x.de/x-x-x-x-x.html
wstaylor: http://www.wstaylor.net/vista_walls.htm
VistaThemes: http://www.vistathemes.org/
VistaKnowlodge: http://www.vistaknowledge.com/
Trucsenvrac: http://www.trucsenvrac.com/
CrystalXp: http://www.crystalxp.net/
IconEasy: http://www.iconeasy.com/
Iconspedia: http://www.iconspedia.com/
DeskmodBR: http://www.deskmodbr.com/
H2O DeskMod 2010: http://h2odeskmod.wordpress.com/
Tech4PC: http://www.tech4pc.net/tag/deskmod-windows-7/
Vista Deskmod 2009: http://vistadeskmod.com/deskmod/
Deskmod Show: http://deskmodshow.blogspot.com/
Defender Team: http://www.defenderteam.com/secao/downloads/deskmod/
Max Deskmod: http://maxdeskmod.net63.net/
DeskMais: http://www.deskmais.com.br/
Windows7 Themes: http://windows7themes.net/


Linux (contribuição de p0int):

gnome-look: http://www.gnome-look.org/
xfce-look: http://www.xfce-look.org/
kde-look: http://www.kde-look.org/
compiz-themes: http://www.compiz-themes.org/
beryl-themes: http://www.beryl-themes.org/

Este tópico irá sendo actualizado conforme disponibilidade.