It's always interersting watching how conversations ebb, flow and seguet on the GDC Listserv. A recent thread yielded this list of recommended apps, extensions and utilities.

1Password: Must-have password/login manager, with nice browser integration and iPhone app.
A Better Finder Rename: file renaming utility.
Blow Up 2 from Alien Skin
Appzapper: Removes programs and all associated files in one “zap”
Adium: Multi-service instant messaging app.
Art Text 2:  good for taking type manipulation farther than Illustrator does
Backblaze: Automatically backups Mac offline ($5/mo server fee), runs pretty seamlessly in the background. Use this in conjunction with Time Machine for local backups.

CadTools: An add-on for Adobe Illustrator that turns it into a pretty decent CAD application (dimensioning tools - assigning different scales - isometric drawings etc., great tool for isometric illustration

Carbon Copy Cloner: drive migration
CDFinder: robust CD/DVD archive indexing
CleanMyMac
ClicktoFlash for Safari, blocks Flash til you choose to load it by clicking it
Connect360: Allows media file sharing between Xbox and Mac
Default Folder.
Disk warrior: Don’t have to use it that often but it has saved me (and some files/photos) more than once
Dropbox: Must-have automatic cloud file storage sync software. 2GB free. Desktop/mobile versions, sync across unlimited devices.
eDocker
Evernote. Great for research and org lists kept in the cloud. iPhone and Dropbox compatible.
Flashblock for Firefox
FontExplorer X Pro: somewhat solid, stable font management
FontXChange:  converts between formats, most often use it to make OpenType versions
Forklift for FTP; it’s the only one I know that let’s me view two FTP sites in one window.
Fotomagico:  quick and easy slide transitions
Graphic Converter X: opened a couple of strange image files where Photoshop failed
Hyperdock

Inspiration explorer - iPad app

issuu.com

iStat Menus: System diagnostics visualizer. See how your machine is working at a glance.
Letterbox: Add on for Mail on OSX, creates three-pane view. Great for wide screen monitors.
LittleSnitch: Blocks software on your Mac from communicating with the mothership or “calling home” unless you let it. Great way to discover spyware/adware, etc.
Morelomo - for  iPhone
OpenDNS: DNS management Popchar is useful until Photoshop gets a (long overdue)
Pageflip
Quicksilver
Renamer4Mac: batch rename files quickl
Scrapbook browser plugin. I like to Scrapbook all my online purchases and official e-docs.
Scrivener: low-cost writing software that is intuitive, can be as unobtrusive as you want it to be, but also has some super-handy file organizational tools.
Simplenote and Notational Velocity. It’s the same kind of synced-everywhere note taking system as Evernote, but strictly limited to plaintext, rather than allowing you to upload images, make nicely-formatted lists, etc. The idea is that a more full-featured process would require more overhead, while reducing the utility offered by plain text.
Smart Scroll: iPhone-like smooth scrolling.
SneakPeak Pro.
Sound Studio: simple to use. Join sound files, fadein, fadeout, done.
Stair Interpolation Pro  Fred Miranda’s upsampler for Photoshop which works way better than Genuine Fractals or Photoshop’s native and is much cheaper!
Super Duper: Backup software. AWESOME. Use it in conjunction with Time Machine (partition your backup drive).
Tex-Edit Plus: lean, fast text editor, great for stripping unwanted formatting
Tooble: can’t get enough of that YouTube video? There’s a tool for that.
Transmit:  FTP/SFTP client
Visual Thesaurus: dynamic dictionary and thesaurus, on steroids. Useful for ideation
VLC: view almost all Windows and Mac video files

Webmail interface from Google Apps’ for daily mail, with images and html signatures, check out the “canned response” labs plug-in. Not as direct as a standard signature, but gets the job done.
WireTap Studio: grab any sound from any source for presentationswebmail interface for daily mail, with images and html signatures, check out the “canned response” labs plug-in. Not as direct as a standard signature, but gets the job done.