I am slowly converting all my Linux and some of my Windows machines to Gentoo. The following is a list of my "must have" packages before you install anything else.

• ccache - this caches compiled code, so if the compiler is calling for some code and it already has been compiled then it comes from the cached. This really speeds up subsequent compiles. Install this first.

• esearch - nice command line package search
  
  
• gentoolkit - portage tools
  
  
• kuroo - if you are using KDE (and why wouldn't you - Gnome is technically inferior :-) Kuroo is a portage tool which simplifies package management. It also includes Gentoo Watcher which monitors packages for currency and notifies of security advisories.
  
  
• krusader - Total Commander like tool for KDE