With developers now tearing up the Windows 8 developer preview and looking for hidden gems, we're going to soon see an amazing number of utilities aimed at improving the Windows 8 experience and, in some cases, making it work more like its predecessors. While I can't endorse or support that kind of thing, let alone recommend individual utilities quite yet, I figured it would be useful to collect what's out there in a single location.
Here's what I've found so far. If you find a Windows 8 utility that's not listed here, let me know and I'll see about adding it to the list. (Newer utilities are listed at the top.)
Added September 25, 2011
This utility lets you change the wallpaper (what Microsoft calls the "accent") of the Windows 8 Start Screen and logon screen.
Added September 24, 2011
This utility provides a number of interesting features, including the ability to unlock hidden Windows 8 Developer Preview features and find and install pre-release versions of the next Microsoft Office. I have not tested this utility, so please proceed at your own risk.
Download (Page is in Italian)
This utility allows you to toggle between the Metro Start screen and the Classic start menu in Windows 8 Developer Preview. 
Disable Metro Start Screen. Disables only the new Start screen.
Disable Metro Ribbon. Disables only the Metro Ribbon UI.
Disable Metro Start Menu and Ribbon. Disables the Metro Start screen, Ribbon UI, Metro Task Manager UI and the Lock Screen.
Enable Metro Start Menu and Ribbon. Re-enables all available Metro UI options.
Add Power Options to the Metro Start Screen. Adds Logoff, Switch User, Lock, Sleep, Restart and Shutdown tiles.
Add any Application/File to the Metro UI Start Screen. Allows you to add those apps and files that may not be normally available to you to the Start screen.