Free antivirus software
Avast http://www.avast.com/free-antivirus-download-b
Avira http://www.free-av.com/en/download/1/avira_antivir_personal__free_antivirus.html
AVG http://free.avg.com/ww-en/download-avg-anti-virus-free
PCtools http://www.pctools.com/free-antivirus/
Clamwin: http://www.clamwin.com/

Free online antivirus system scans
F-secure http://www.f-secure.com/en_EMEA/security/tools/online-scanner/
E-set http://www.eset.com/online-scanner
Bitdefender http://www.bitdefender.com/scanner/online/free.html
Symantec http://security.symantec.com/sscv6/home.asp?langid=ie&venid=sym&plfid=23&pkj=WHQRRHYTINMHDKDCWLL
Trendmicro http://housecall.trendmicro.com/
McAfee http://home.mcafee.com/downloads/freescan.aspx
Submit single file for scan at Kaspersky http://www.kaspersky.com/scanforvirus
Scan for viruses & spywares using Microsoft's Onecare Safety Scanner

Antispyware
Spybot search & destroy http://www.safer-networking.org/en/download/index.html
Lavasoft Adaware http://www.lavasoft.com/products/ad_aware_free.php
Spyware doctor (from Google Pack) or PCTools

Firewall
Comodo: http://personalfirewall.comodo.com/
Zone Alarm: http://www.zonealarm.com/security/en-us/zonealarm-pc-security-free-firewall.htm
PCTools: http://www.pctools.com/firewall/

PDF reader
Foxit: http://www.foxitsoftware.com/pdf/reader/
Adobe: http://get.adobe.com/reader/

Image viewer
FastStone Image viewer: http://www.faststone.org/FSViewerDetail.htm
Irfanview: http://www.irfanview.com/

FTP software
Filezilla: http://filezilla-project.org/download.php
CoreFTP: http://www.coreftp.com/
CoffeeCup: http://www.coffeecup.com/free-ftp/

Internet Browsers
Microsoft Internet explorer 8: http://www.microsoft.com/windows/internet-explorer/default.aspx
Mozilla Firefox 3.6: http://www.mozilla.com/en-US/firefox/firefox.html
Google chrome 5: http://www.google.com/chrome/intl/en/landing_chrome.html?hl=en
Opera 10.53: http://www.opera.com/download/
Apple's Safari 5: http://www.apple.com/safari/download/

Email clients
Mozilla Thunderbird 3: http://www.mozillamessaging.com/en-US/thunderbird/
Incredimail : http://www.incredimail.com/english/splash.aspx
Pegasus mail: http://www.pmail.com/downloads.htm

Document editors
Openoffice: http://download.openoffice.org/
Lotus Symphony : http://symphony.lotus.com/software/lotus/symphony/home.nsf/home
Google docs (online): http://docs.google.com/
Microsoft Live office (online): http://login.live.com/
Adobe Acrobat (online): https://acrobat.com/

Media/Video players
VLC media player: http://www.videolan.org/vlc/
K-lite codec pack with player: http://www.free-codecs.com/k_lite_codec_pack_download.htm
Winamp: http://www.winamp.com/media-player/en
Real player: http://in.real.com/
Divx Player: http://www.divx.com/en/software/divx-plus/player
Apple's Quicktime player: http://www.apple.com/quicktime/download/