Since the day I moved to the Mac I was impressed not only by the quality of the operating system but also by the quality and good looks of most of the programs (and their icons) I've started using. Below is a list with some amazing icons from the apps I use on a regular basis. Feel free to suggest your own.
Description: Small utility that lets you track apps and their licences. Very useful.
Description: My HTML / CSS editor of choice - most of the times I have no need for external apps to build web sites. It has an integrated FTP client and the logo / icon is just awesome.
Description: Small app that uses various algorithms to find matching colors.
Description: By far the best CSS editor on the mac
Description: Capable HTML / CSS editor - not as finished as CSS Edit but quite usable.
Description: Free utility from Garmin for my Nuvi
Description: A quite capable screen & website capture utility - very handy to capture full page screenshots
Description: An email client specifically built for multiple gmail accounts. I use this all the time.
Description: A very fast and capable image editor
Description: A very capable email client - very fast and has some nice, unique features.
Description: A task manager I can't live without
Description: A unique screen grabbing utility - very handy when chatting with clients and sharing comps instantly
Description: One of the best FTP clients for the Mac
Description: Twitter app for mac and iphone - the best twitter experience for mac (in my opinion)