MacPilot is another good option for fiddling around with your Mac, optimizing it to run better and unlocking the hidden potential of OS X and many applications--all without having to use the command line. MacPilot's graphic interface and file browser give you access to an almost staggering number of customizations, commands, key combos, and more, all organized around specific applications (include Apple and some third-party apps) as well as categories like Disks, Startup, Logs, Tools, and Power. You can do everything from changing the boot mode (64-bit or 32-bit) to tweaking the behavior of the Finder and Dock to activating hundreds of "secret features" in many apps (whether you want to, say, disable inline attachment viewing in Mail or automatically grammar check your Web forms in Safari). You can also search for features within a given app or category using a search bar, and browse through popular or favorite features.
There are other cheap--and even free--options out there with similar functionality, so try out a few just to make sure you're getting the features you want. Fortunately, MacPilot comes with a no-limits 15-day trial.