Portage:

• Remove many duplicate packages of an older version (example code here: remove kde 3.2.3 after kde 3.3.0 was successfully installed and tested) for p in `qpkg --dups -v -nc | grep kde.*3\\.2\\.3`; do emerge unmerge =$p; done;
• For quick lookups which packages exist (with installed version, masked versions, slots,...) use app-portage/eix simply add /usr/bin/update-eix > /dev/null to your emerge --sync cronjob

Linux:

My most used shell-tools in linux are app-misc/screen, www-client/elinks and net-ftp/lftp