The Dock is an integral part of OS X that Apple has styled in a one-size-fits-all manner. While the feature does work well, Apple's approach has kept a number of people at odds when features of the Dock have changed. For instance, in Leopard when Apple added reflections and changed the indicator to a white dot, many people found the view to be rather unappealing.
Over the years there have been several methods for customizing aspects of the dock, some of which that we have covered here at MacFixIt; however, most of these have been on Dock organization features and not so much the aesthetics of the Dock.
Recently a small utility called "Docker" has come to my attention, which offers a number of customizations for the Dock, to make it look exactly how you want it to look. You can change the color, the transparency, the indicator style, and the separator style, all to make the Dock look and behave differently without affecting the functionality of the Dock.
The developers have looked into all options for the Dock, and give them to you in a relatively intuitive interface. Docker separates Dock settings into several groups, each which tackles a different aspect of the Dock: Styles & Colors, Settings, Stacks & Spacers, Kiosk Settings, and Locks.
Styles & Colors
This is perhaps the most useful aspect of Docker, where you can change the indicator style to be any color you want, or change it back to the arrow as it was in pre-Leopard versions of OS X. The same goes for the Separator and the outline when the dock is in 2D form. For the 3D Dock, the ability to remove reflections is something a number of users have desired.
These cover the basics that Apple already provides (ie, size and magnification) along with several other options. These include placing the Dock at the beginning or end of a screen edge, rather than just in the center, using additional minimize effects and icons, and changing the bounce and spring-loading behaviors of the Dock contents.
Stacks & Spacers
This section contains exceptionally useful organizational settings, allowing you to add specialty stacks and modify highlighting behaviors in stacks, but the most useful seems to be the addition of Dock spacers. This is where a blank space is placed in the Dock, which will allow you to better group items in the Dock. Granted doing this can splay out the Dock, which might be undesirable for some people, but I find it to be exceptionally useful.
This section allows you to set the behavior of the system menubar, hiding it when certain applications are open, and also changing its behavior when using the Finder. Unless you use the computer in a public environment, I'm not sure what use this would bring, but it's there in case you want it.
The last section in Docker allows you to lock various aspects of the Dock, including the contents, its size and position, the magnification and minimization settings, and it's autohide behaviors, preventing you from inadvertently changing the dock by accidentally removing an item. Some lockable items seem unnecessary (ie, minimization effects), but they're there to be locked if you want to.
I've been using Docker for a few days now, and in both my Leopard and Snow Leopard systems the program seems to do what it advertises with no adverse effects. You launch the utility, make changes and click "Apply", and the Dock will be relaunched with the new settings. The program does modify the contents of the Dock application itself, which kept me skeptical at first, but it appears to only manage a few image resource files that the Dock uses for backgrounds and indicators. The rest is done through the Dock's preference and database files.
Since the program does modify the Dock itself, I strongly recommend that if you use the program to first ensure you have a backup of the Dock. The easiest way to do this is to go to the /System/Library/CoreServices/ folder and zip up the Dock using the "Compress Dock" contextual menu option. From here, you can always restore the Dock by uncompressing the zip file and replacing the modified Dock with the backup.
Docker is donationware, meaning you can use it free of charge with the option to donate to help support its development. It currently at version 1.6.4 which added compatibility options for Snow Leopard, and can be downloaded from the developer's website: http://www.blocksoft.net/docker.html