Macbook Pro is my system of choice for all computing (blogging, coding and otherwise) – 8MB, 2.4 GHz Intel Core 2 Duo.
I edit posts in TextMate as a first draft and copy/paste into the HTML editor in WordPress for final adjustment.
OmniGraffle is an awesome tool which I use for creating artwork as well as building application wireframes, technical specifications and the like.
Seashore is an open source image editor that I use regularly for basic graphic manipulation.
As a replacement for the Mac integrated terminal, I prefer iTerm2, which is a must for those of us who grew up with the command line.
Applescript, Bash and Python are a few of my personal favorites for general tinkering.