A buddy of mine, Gil Rutkowski (@flashingcursor), is in the process of switching over to OSX. Both to help him, and serve as a quick reference for myself, I compiled a quick list of my favorite OSX apps. Maybe it contains some hidden gems to you!
I left out apps that are no brainers – Apple Apps, MS Office, text editors (TextMate, Sublime Text 2, CSSEdit), Adobe products, etc. I’m sure some apps I use are not listed, this is just off the top of my head!
RC DefaultApp – easily control your default apps via the system preferences.
Growl – system-wide notifications.
Transmit – FTP, SFTP, mount as drive, etc (this can replace ExpanDrive). Best FTP client available.
1Password – manage all your passwords. Integrates into all browsers, apps for all devices, syncs with DropBox.
Alfred – preform quick searches on your computer and google. Time saving app and a must have.
PathFinder 5 – The ultimate Finder replacement. Apple should really buy them and integrate this. Once you use it you will never go back to the plain finder
Adium – OSX equivalent to Pidgin.
Burn – free powerful burning app.
Textual or Colloquy – IRC clients. Also look into xChat.
iTerm 2 – powerful terminal replacement.
Versions – if terminal-based SVN isn’t your thing
GitHub OSX client - ’nuff said.
Divy – resize and move windows to a grid, quickly.
Fluid App – wrap websites in an app (such as Google Calendar).
Mailplane – App for Gmail/Google Mail.
Dropbox – duh!
VLC 2 – duh!
FileShuttle – lets you upload files to s/ftp (screenshots, etc) instantly and creates short URL automatically.
LittleSnapper – Capture websites for inspiration, store in a library which can be sorted, rated, etc. Can be synced with Dropbox.
Notify – I use gMail for my client, but Notify is a great addition for alerts.
SuperDuper – create *bootable* backups. Must have.
TextExpander – stores snippets, great for canned email responses, chunks of code, etc. Can be synced with Dropbox.
iStats Menu – keep an eye on stats from the menu bar.
Transmission – speedy torrent client.
SequelPro – GUI client for MySQL
Chicken of the VNC – VNC client, works flawlessly.
coconutBattery – monitor batter health.
Disk Inventory X – monitor disk usage.
HandBrake – Rip DVDs to xvid/divxh264/etc.
MacTheRipper – DVD extractor.
UnRarX – easily handle .rar files.
MAMP – Both free and pro versions work well. Take your pick.
AppTrap – when you delete an application, logic says it should uninstall. Unfortunately that doesn’t happen by default, this fixes that problem.
Last updated: Feb 2012

You’ve saved me days of searching and testing… and saved my twitter followers from many #macnoob questions. Beers on me next time we hang out!
Great list, even if it was done fairly quickly. Always curious to see the “must haves” because each person has a few gems in there.
MAMP/MAMP Pro – for setting up localhost environments (http://www.mamp.info/en/index.html)
Carbon Copy Cloner – Alternative to Superduper (www.bombich.com)
I also like Mirro http://www.getmiro.com/ for video conversation, also handbrake is sweet too.