There are a ton of great pieces of software that have been developed by the OSx86 community. Some are GUIs for simple Terminal commands, and others are 1 function scripts. The following list includes some my favorite free tools.
Installs kexts one at a time, and does 'full service' Extensions.mkext creation. The best feature of Kext Utility is its interface to create caches- you simply drag the Extensions folder directly on top of the icon in /Applications folder or Dock.
Developer: Open source script
Handy 1 function script app. ShowAllFiles enables view in Finder of all hidden files. Very useful for locating hidden boot files, mach_kernel, etc... The latest version works in Snow Leopard.
Code editor specifically for DSDT.dsl files. DSDTSE does full service extract/compile of DSDT.aml files. It also features a DSDT editing guide built-in, with copy/pasteable code snippets, color coding, and search functionality.
Kext Helper b7
The drag n' drop kext installer Kext Helper b7 lets you install multiple kexts at once, and also repairs kext permissions and creates a script to tag cache rebuild.
Developer: PCWiz Computer
An all-in-one utility, OSx86Tools installs kexts, kernels, creates and deletes caches, automatically installs EFI boot strings, and much more. Some features such as About This Mac and CPU information editing are buggy in Snow Leopard. Not currently under development.
Developer: Charles Srstka
Not technically an OSx86 community project, but honorable mention goes to the shareware application Pacifist- which allows you to extract OS X Package files to show, download, change and install contents. You can also open Apple Install Discs and URLs.
If any of these pieces of software have helped you, or you have ideas for additions to this list, post in comments. Have fun!