Audio / Video
VideoLan (VLC) – My Windows video player of choice. This free program can play almost any video format and it is open source.

Web Browsers
Mozilla Firefox – Firefox is an excellent free IE  alternative. It is incredibly personalisable with themes and extensions. Install popular extensions NoScript and AdBlock Plus and you will have a much more secure browser.

Google Chrome – A faster web browser and one that I am currently preferring over Firefox. Chrome’s speed makes browsing the web much more enjoyable and it’s syncing across multiple systems is perfect when you use multiple computers/devices.

VOIP / Instant Messaging
Skype – The most popular video chat client in the world. Free Skype to Skype calls and low mobile call rates make Skype a great choice for VOIP. It also has a chat system built in.

System Protection
Avast – Yaarr pirates (read viruses) stand little chance when avast is protecting your system. Use in combination with a Malware scanner to secure your system.

MalwareBytes Anti-Malware – Speaking of Malware scanners here’s MalwareBytes. An excellent supplement tool to your virus scanner of choice.

System Maintenance
CCleaner – Occasionally temporary files build up, your registry gets bloated and your internet tracks need erasing. Crap Cleaner does this and does it well.

Image Manipulation
Adobe Photoshop – Has that been photoshopped? This is still my image editor of choice.

Office
Microsoft Office 2010 – The most well-known Office application suite. Personally I still prefer 2007 but since you cannot buy it new anymore 2010 will have to do. Once you get the hang of the toolbar layout it isn’t too bad.

Backup Solutions
Crashplan – Offers local, offsite and cloud backup solutions.

Miscellaneous
uTorrent – A lightweight torrent client for all your *ahem* legal downloads.
FileZilla – Any webmaster worth their salt would use FileZilla or WinSCP to satisfy their FTP needs.
TeamViewer – Handy tool if you need to remotely control your desktop while away.
Izarc – Free and superb extracting software. Winzip, Winrar etc have nothing on this

Audio / Video
MPlayerX – If not the best, one of the best free Video players on OS X. I used to use VLC but this is faster and works flawlessly.

iTunes – On OS X iTunes is pre installed and if you have any iDevices it is the obvious choice to get music transferred across to them. I find it bloated but it does organise music well. Until I find a better alternative iTunes will be my music player on OS X.

Web Browsers
Mozilla Firefox – Firefox is an excellent free Safari alternative. It is incredibly personalisable with themes and extensions. Install popular extensions NoScript and AdBlock Plus and you will have a much more secure browser.

Google Chrome – A faster web browser and one that I am currently preferring over Firefox. Chrome’s speed makes browsing the web much more enjoyable and it’s syncing across multiple systems is perfect when you use multiple computers/devices.

VOIP / Instant Messaging
Skype – The most popular video chat client in the world. Free Skype to Skype calls and low mobile call rates make Skype a great choice for VOIP. It also has a chat system built in.

System Maintenance
AppCleaner – I no longer uninstall programs by deleting them from the Applications folder as this leaves their temporary or config files behind. Instead use AppCleaner to eliminate all traces of the undesired application.

Image Manipulation
Adobe Photoshop – Has that been photoshopped? This is still my image editor of choice. It is quite pricey so if you’re looking for a free alternative try Gimp for Mac

Picasa – A great picture library / manager. In my opinion it is better than iPhoto and if you want it can sync with the Google+  social network

Office
Microsoft Office 2011 – I’m preferring this over iWork as I’m more familiar with Microsoft’s Office Suite. Not a fan of Outlook in this package however and prefer to stick with Mail as my email client.

Backup Solutions
Time Machine – Built in to the OS X (10.5+) Operating System, this software can back-up your entire system to an external hard drive or time capsule. If you need offsite backups try CrashPlan.

Miscellaneous
uTorrent – A lightweight torrent client for all your *ahem* legal downloads.
FileZilla – Great FTP application for webmasters.
TeamViewer – Handy tool if you need to remotely control your desktop while away.