I still have a soft spot for the "brushed metal" appearance available in Mac OS 10.4.

It may have been over the top, but it looked so cool. And it did tricks that made it very difficult to replicate on other platforms of the time, including multiple transparent layers and dynamic gradients to create fake "lighting" effects on the metal.

One of these days I need to put together a realistic CSS take on it; it should be doable now, but it certainly wasn't in 2006.