Note: The applications are not listed in any particular order.
Windows
Pretty standard applications I must say.
1. WinZip
2. Trillian
3. Paint Shop Pro
4. GetRight and CuteFTP or FileZilla
5. Java
6. mIRC
7. Acrobat Reader, AbiWord & OpenOffice.org
8. Nero
9. Mozilla/Firebird and Opera
10. Media Pack (WinAMP, DivX, QuickTime, VLC and Real)
Unix/Linux
On Linux, most distros already come with these following applications, but on other Unices they don't always come as standard as they are not part of X, Gnome or KDE. If that happens, here's what I try to get for these systems:
1. Gaim or Kopete
2. K3B
3. OpenOffice.org & AbiWord or KOffice
4. 'Downloader for X' and gFTP
5. RDesktop & tsclient
6. The Gimp
7. X-Chat
8. Media Pack (VLC, Ogle, MPlayer, XMMS and Xine w/ Totem)
9. Quick Lounge for gnome-panel
10. Ximian Evolution
Mac OS X
I wrote a more comprehensive Mac OS X application list the other day, but this is my really-must-have list.
1. Fire
2. Transmit, Speed Download or iGetter
3. DiscBlaze
4. Media Pack (MacAMP Lite, VLC, MPlayer, Micorosft Media Player)
5. X-Chat Aqua
6. Microsoft Remote Desktop Connection
7. CodeTek VirtualDesktop
8. USB Overdrive X
9. Photoshop Elements or GraphicConverter or MacGimp
10. Watson
BeOS
I don't use BeOS much anymore (maybe one or two reboots per month), but here is my list. You can see screenshots and more info about these apps on BeBits or BeZip.
1. ProcessController
2. VLC
3. ArtPaint or Refraction or Becasso
4. Helios CDRecorder
5. OpenTracker
6. BeShare
7. BePDF
8. SoundPlay
9. Bezilla or Firebird
10. Vision
BeOS 5 hasn't been updated for quite a long time and so the OS itself doesn't come with a lot of stuff resulting in the need to download more third party applications in order to get a more complete experience. Here are some more apps that I usually need to install under BeOS.
11. NetPenguin and BeGet
12. Gobe Productive
13. 'Terminal Here' Tracker addon
14. GifTranslator and ImageViewer
15. GimICQ, Y!, MSN and AIM clients



