Skins and other art for PC:

DeviantArt - An Art Community, with good works of almost all computer graphics related.

OSXP - A place where you can get many good things for skinning related, like DesktopX.

ArtUproar - A site containing many skin related files, for many applications.

Studiotwentyeight - A good source for icons and visual styles, check it out.

Playboy Skins - A nice website offering skins and visual styles as well.

Icon Related:

My Icons on DA - Here is a place where you can see my icons, at DeviantArt.

VisualPharm.com - Personal web site of an XP icon designer for commercial purposes.

Graphics Related:

RoboUK - A good source for Photoshop related tutorials and other applications too.

Misc

Talisman - A Program which replaces desktop adding some cool functions.

MacThink.net - A new Mac OS X visual emulation community for Spanish talking community, a must check if your language is Spanish.

Iceman's Emulation - A good page to the mac graphic emulation on PC.

Links