Themes, Graphics, and Icons

Belchfire.net
Windows XP Themes, LogonUIs, bootscreens, and wallpaper.
http://themes.belchfire.net/

Bfarber.com
Collection of login screens and visual styles for Windows XP, as well as wallpapers and small freeware applications.
http://www.bfarber.com/

Desktop Rating
Rating site where you can post, rate and comment on themed desktop screenshots.
http://www.desktoprating.com

FolderIcon XP
Icon changer, select one of 129 specially designed XP-style icons, colored, numbered folders or use any external icon. Extendable set of 262 specially chosen system icons is installed. [Shareware]
http://meaningdata.com/foldericon/

GetSkinned.org
Offers desktop themes, login screens, boot screens, wallpapers and icons. Encourages people to submit more wallpapers and themes.
http://www.getskinned.org/

Glyph Lab
A selection of XP and Vista style toolbar and web icons, also offering a full custom design service.
http://www.glyphlab.com/

GroovyThemes
Collection of themes, graphics and wallpapers.
http://www.groovythemes.com/

Guiicons
Provides XP icons for commercial manufacturers.
http://www.guiicons.com/

Icon Galore
Offers professional XP style icons for use in websites, software, multimedia, print and web based applications.
http://www.icongalore.com/

Iconica
Offer custom Windows XP icons created for software or web developers, stock icons, toolbars strips, logos, graphic design and illustration.
http://www.marvilla.us

IconPharm
Royalty-free icons for commercial software manufacturers.
http://www.iconpharm.com/

I-cons
Features icons and tools.
http://members.xoom.alice.it/i_cons/

Logolando
User account logos for Windows XP.
http://hem.passagen.se/bence/

Mac OSXP
Wallpapers, skins, icons, and other graphics to make Windows XP look like Mac OSX.
http://www.geocities.com/xpmp8/

Star Wars Faces
Collection of Star Wars characters for use as User Account Pictures.
http://web.ukonline.co.uk/starwarsfaces/

Studio 28
Visual styles, icons and wallpapers.
http://www.studiotwentyeight.net/

ThemeXP
Offers desktop themes, login screens and wallpapers to fully customize user's computing environment.
http://www.themexp.org/

WBC Icons
Free 32 bit alpha blended icons for Windows XP. Includes a tutorial section on icon creation.
http://icons.wbchug.net/

Windows Icons
Professional icons based on the Windows XP icon style.
http://www.windows-icons.com/

XPLogos
Check out this collection of User Account Pictures. Includes a tutorial on how to change the pictures.
http://www.xplogos.com/

XPThemes.com
Features visual styles, themes, wallpapers, cursors, logon screens, customization software and articles.
http://www.xpthemes.com/