Must Have's

Antimalware from MalwareBytes.org
Firefox from Mozilla
WOT (Web Of Trust) add-on
NoScript add-on
CCleaner from Piriform
Roboform from Siber Systems
Adobe Reader from Adobe
Secunia Personal Software Inspector from Secunia

There are other programs that I use but these are the ones that, for me, are essential.

PerfectDisk
Shark007 Codecs
paint.net
7-zip
notepad++
filezilla
putty
recuva
steam
MSE
Windows Live Essentials
CCleaner
Winamp
Foxit reader
MS Office
Firefox
WinPatrol

Hmmm,

These are always my first installs after a fresh OS install.

Ms Office
Adobe CS4
Power ISO
Paragon Partition Manager
Nero 9
VMworkstation
Audible books Manager
U Torrent
Acoustica CD/DVD Lable Maker
Winrar
Djview
Acronis Backup and Recovery.

The KMPlayer
Handbrake
InfraRecorder/Imgburn
Real Alternative
RealVNC
MediaMonkey
DVD Decrypter/DVD Shrink
iPhoneBrowser
WBFS Manager
Picasa

Plus many that have already been listed.

Lots of unnecessary software here. I would:

Gaming PC:

Nothing - except drivers, updates and 3D Mark Vantage/PC Mark Vantage

Other PC's:

Foxit Reader - Adobe is fat junk
K-Lite Basic Codec Pack (just ffdshow and 3 other tools really)
Teamviewer 5
MSE or another suitable app, no need for more antimalware tools
HD Tune
Keepass
Adobe Flash
DivX Web Player (if necessary)
Drivers + Windows Updates
Secunia PSI

My short absolutely must have list:

MS Office
Firefox
Thunderbird
paint.net
CDBurnerXP
Winamp
IZArc
Speedfan
GFI Backup
Notepad++
Gadwin Printscreen
MSE
LCD Smartie

- Chrome
- Winrar
- Photoshop CS4 (or another image editing program)
- Winrar
- Messenger
- Utorrent
- SIW
- PowerISO
- Notepad++
- Avast! [Free]
- Lots of codecs
- Mysticthumbs
- Restorator
- Librarian
- Office package (MS office or Openoffice)