On going list of Mac OS X software i use

[Cow4prez]

Some are free, some are not. Usefulness mileage will vary

resistulator (very useful widget) http://www.zambetti.com/projects/resistulator/
eagle (make schematics and PCB layouts)
intaglio (useful drawing program)
crossover - run your win xp on mac os x ( a little buggy)
iwatermark - mark your schematics for copyright (nice)
mac the scope (not working well)
macspice
flickr uploader - transfer files to flickr account (photos, gif etc)
diy layout creator java version (buggy)

[Cow4prez]

Electricalc 2.0.1
http://www.macupdate.com/info.php/id/6935/electricalc

[RnFR]

there is also Osmond PCB.

[culturejam]

I use OmniGraffle Pro to draw schematics. It's not free, but you can download a trial. *mumble mumble* serial number *mumble*

[modman]

Some are free, some are not. Usefulness mileage will vary

resistulator (very useful widget) http://www.zambetti.com/projects/resistulator/
eagle (make schematics and PCB layouts)
intaglio (useful drawing program)
crossover - run your win xp on mac os x ( a little buggy)
iwatermark - mark your schematics for copyright (nice)
mac the scope (not working well)
macspice
flickr uploader - transfer files to flickr account (photos, gif etc)
diy layout creator java version (buggy)

thanks for iwatermark

I also use a lot of Linux based open source stuff such as:
Openoffice.org
Gimp.org
all free, open source and perfect clones of Office or Photoshop, designed and maintatained by a community of users. Sounds familiar, no?