Bash
- ss64.com/bash - well-written compilation of command references.
- command-not-found.com - for those times when the command is not found.
- explainshell.com - explains shell commands by breaking them apart.
- tldr.sh - a neat alternative to raw
manpages. - #bash FAQ - tips compiled from the #bash Freenode IRC channel.
- .bashrc PS1 generator (bashrcgenerator.com) & Bash $PS1 Generator (kirsle.net) - generate the code to configure the display of your bash prompt.
- bitbucket.org/snippets/200ok - includes things like 'git bling' for PS1, helper scripts, etc.
Shell scripting
- Google's Shell Style Guide
- shellcheck.net - validator/linter for your shell scripts.
- BATS - write tests for your shell scripts.