The Basics
Chrome - needs no introduction
Iterm2 - far better terminal program than the built-in version. Supports panes and tabs and a bunch of other nice features.
Ack - a superior version of grep - highlights matches, recursive by default, etc. This is my goto tool for finding stuff in sourcecode.
The installation one-liner:
/usr/bin/ruby -e "$(/usr/bin/curl -fksSL https://raw.github.com/mxcl/homebrew/master/Library/Contributions/install_homebrew.rb)"
Then you need build tools (gcc, etc). You can install these through XCode (the "normal" way), or by using osx-gcc-installer.
XCode is a massive 4.7G download, but it's a requirement for iOS development so I need it anyways.
With XCode: App Store Link, then open XCode and go to Preferences -> Download -> Install Command-line-tools
Without XCode:
If you don't need the full XCode GUI, the osx-gcc-installer is a DMG installer for just the command-line tools. It's much smaller and quicker to get going. Also doesn't require an Apple Developer account.
My Brews:
ack curl git-subtree gnu-tar jpeg node xmlto
asciidoc docbook gnu-getopt imagemagick libtiff pkg-config xz
coreutils gettext gnu-sed jasper little-cms wget
Vim
PCKeyboard hack (CapsLock --> ESC): http://pqrs.org/macosx/keyremap4macbook/extra.html
https://github.com/ddopson/home
Node.js
http://nodejs.org/#download
See my other post
underscore-cli - great tool for parsing and processing JSON data
jshint - more configurable version of JSLint