To find the current set of dock images navigate to:
/System/Library/CoreServices/Dock.app
ctrl click on dock.app and select “Show Package Contents”.
Then Navigate to:
/Contents/Resources/
Then dig through folder to find these 4 .png’s:
scurve-l.png
scurve-m.png
scurve-sm.png
scurve-xl.png

Now drag a copy of them to your desktop, whip them into Photoshop, and create your own custom dock.

After you have something wickedly awesome, make a backup of the original files, and then copy the edited ones into the Resources folder to replace the standard ones. Restart the dock with the terminal command killall Dock, and you should be all good to go.

My personal favorite customization, so far, is the smoke dock… which is sadly no longer available, though it wouldn’t be the hardest thing to make in Photoshop. Here is what it once looked like: http://gadgets.bligblog.com/5562/smoke-glass-dock/. One of my friends downloaded the .png’s for the ‘smoke dock’ before the site went down. I will try to get them up here.

Here are some other ideas for it:
http://theappleblog.com/2007/10/31/create-sky-and-wood-custom-dock/

If you make a cool design for the dock and want to share, link to me or drop me a comment, and I will add your link/site/design to the ones listed here.

Many people have complained about the new dock in leopard and all it’s eye candy… Personally I kinda like it except that it has way to much going on. The reflections from the icons are nice…but they conflict visually with the wavy, stylized glass line through the middle of it… add some more reflections from all other windows, a 3D tilt, and just a hint of shadow… and you’ve got some major visual anarchy going on.

Now being an artsy kind of person, I like sexy UI’s, even if they have visual features that don’t do anything but just look good. However, the Leopard dock is just annoying. They should have either chosen reflections, or picked the fake OS X glass look… but not both.

Anyway enough complaining…
Jordan.action.rant = False;

I have found the solution to the problem: Turn off the glass and discover the sexy dock hidden underneath.

This is actually fairly easy to do. Just open up a Terminal window and run this command:

defaults write com.apple.dock no-glass -bool YES

and then restart the dock:

killall Dock

and BAM!

There’s the hot, new Dock.

If the new dock isn’t to your liking… simply run the same command again, except change the YES to a NO.

-Update-
A friend showed me this other dock hack today… If you like the 3D look, but want less anarchy…this is a good fix.
http://www.blambert.co.uk/smokedock/
-Update2-
This guy’s site is apparently not working anymore(my guess is that maybe his monthly transfer was used up?)… which is quite sad. Here is what it looked like: http://gadgets.bligblog.com/5562/smoke-glass-dock/
-Update3-
Well, the dock hacks continue. Read more here.

Also, since we are talking about pros and cons of Leopard, here are a few good reads…
DaringFireball.net – A good, solid review
arstechnica.com – A highly detailed look at Leopard
ThinkMac.co.uk – A funny UI rant
Macworld.com – A good pro/con review of features