Andy Miller: Using Sublime Text 2 for Development (Rocket Theme)
Some good tips for getting started with Sublime Text 2 and using its many features.
Neil Gee: Install and configure Apache, MySQL, PHP on OSX 10.8 Mountain Lion
Thats it you now have the native AMP stack running ontop of the Mountain Lion.
Font Matrix
"Matrix of fonts bundled with Mac and Windows operating systems, Microsoft Office and Adobe Creative Suite."
HTTP Client
"A Mac OS X Leopard developer tool for debugging HTTP services by graphically creating & inspecting complex HTTP messages."
ies4osx
Run IE5, 5.5, 6, and 7 in OS X under X11 emulation. It actually works perfectly and installs in minutes with a few clicks.
Paparazzi!
Free Mac software for taking webpage screenshots. Can capture the entire length of a page (beyond the "fold").
urlgreyhot: OmniGraffle Wireframe Palette
An excellent resource for wireframing.
Sakuzaku: I Am Building Ruby, Rails, Subversion, Mongrel, and MySQL on Mac OS X -- Automatically (And So Can You!)
Like it says, a shell script to automatically install the perfect Ruby on Rails development environment on OS X. Useful!