Learn To Detect Viruses And Spyware - Limewire Kazaa Emule

Multiscan
http://virusscan.jotti.org/
http://www.virustotal.com/en/indexf.html

Scan Everything
http://bitdefender.com/scan8/ie.html
http://www.pandasoftware.com/products/activescan.htm
http://avast.com/eng/avast_4_home.html
http://us.mcafee.com/root/mfs/default.asp
http://housecall.trendmicro.com/
http://security.symantec.com/sscv6/default.asp?langid

ie&venid
sym
http://windowsecurity.com/trojanscan/
http://www3.ca.com/securityadvisor/virusinfo/scan.aspx
http://nod32.com/home/home.htm
http://f-prot.com/download/home_user/
http://safety.live.com/site/en-US/default.htm

clamwin doesn't have active scan and it's not too big so you can use it with antivir.

nod32 / avast / kaspersky are probably the best out there.
Blah to avg and mcaffee.


Single File
http://www.kaspersky.com/scanforvirus

Files you shouldn't open without scanning

.bat / pif / com / cmd
.vbs / vbe / vb / bas
.exe / msi
.pif
.bas
.com
.msi
.reg

For safer listening use media player classic, winamp or openvcl. Windows media player and real media player are unsafe due to possibility of macro use inside mp3 files.

The most common viruses are trojans that try to steal personal information, and zombie botnets which spammers use to compromise network servers and send out spam email through them without the user knowing (eating cpu and network resources).

You can also use process monitor to check and see exactly what a file does
http://www.microsoft.com/technet/sysinternals/utilities/processmonitor.mspx