Belchfire.net: Windows XP Themes, LogonUIs, bootscreens, and wallpaper.
Bfarber.com: Collection of login screens and visual styles for Windows XP, as well as wallpapers and small freeware applications.
Desktop Rating: Rating site where you can post, rate and comment on themed desktop screenshots.
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]
FOOOD's Icons: Presents a collection of free icons. Features softwares for changing default icons.
GetSkinned.org: Offers desktop themes, login screens, boot screens, wallpapers and icons. Encourages people to submit more wallpapers and themes.
Glyph Lab: A selection of XP style 32-bit toolbar buttons and icons, also offering full custom designs service.
GroovyThemes: Collection of themes, graphics and wallpapers.
Guiicons: Provides XP icons for commercial manufacturers.
I-cons: Features icons and tools.
Icon Galore: Offers professional XP style icons for use in websites, software, multimedia, print and web based applications.
Iconica: Offer custom Windows XP icons created for software or web developers, stock icons, toolbars strips, logos, graphic design and illustration.
IconPharm: Royalty-free icons for commercial software manufacturers.
Logolando: User account logos for Windows XP.
Mac OSXP: Wallpapers, skins, icons, and other graphics to make Windows XP look like Mac OSX.
Star Wars Faces: Collection of Star Wars characters for use as User Account Pictures.
Studio 28: Visual styles, icons and wallpapers.
ThemeXP: Offers desktop themes, login screens and wallpapers to fully customize user's computing environment.
WBC Icons: Free 32 bit alpha blended icons for Windows XP. Includes a tutorial section on icon creation.
Windows Icons: Professional icons based on the Windows XP icon style.
Windows XP Boot and Logon Screens: Collection of logon screens, wallpapers and logos for Windows XP.
Windows XP Skins: A collection of Windows XP Skins (Visual Styles).
WinXPTheme: Collections of themes, graphics and wallpapers for download.
XPLogos: Check out this collection of User Account Pictures. Includes a tutorial on how to change the pictures.
XPThemes.com: Features visual styles, themes, wallpapers, cursors, logon screens, customization software and articles.