ok some time passed since I wrote my dev setup, so here”s my current one *braindump*

Main Development Setup
Mountain Lion
xCode (or latest iPhone SDK)
Homebrew
Ruby: rvm + rubygems + rails etc.
Database: Mysql 5.1 + Sequel Pro
OpenVPN: Tunnelblick
iTerm 2
Sublime Text 3
Git + GitX (rowanj fork)
FTP & Co: Cyberduck
Hudson status: CCMenu
Share Files: Dropbox
Google Chrome
Safari
Firefox + Firebug

Extended Development
Arduino
Processing
Fritzing
Eclipse

Nice to have:
System Notification: Growl
IRC: hide join messages Adium
Skype
original Twitter client (suxx)
Bowtie
Spotify
All Codecs: Perian
Dasboard widgets: IP + App Update
Copy&Paste History: Flycut
Word replacement: iWork
Apple Mail

Installation hints:

Show hidden files: http://www.mikesel.info/show-hidden-files-mac-os-x-10-7-lion/
Show full dir: http://osxdaily.com/2007/12/02/show-full-directory-path-in-finder-window-title-bars/