Manufacturer's sites

Because searching for the manufacturer's support site often results in third-party sites (that you do not want to visit).  Here are some of the popular actual manufacture sites. 

Manufacture	Home	Support: Help, drivers and software
Acer	http://us.acer.com/ac/en/US/content/home	http://us.acer.com/ac/en/US/content/support
Asus	http://www.asus.com/US/	http://www.asus.com/us/support/
CyberPower	http://www.cyberpowerpc.com/	http://www.cyberpowerpc.com/support/
Dell	http://www.dell.com	http://www.dell.com/support/
Epson	https://epson.com/usa	https://epson.com/Support/sl/s
Fujitsu	http://www.fujitsu.com/us/	http://www.fujitsu.com/us/support/
Gateway	http://www.gateway.com/gw/en/US/content/home	http://www.gateway.com/gw/en/US/content/support-overview
Hitachi	http://www.hitachi.us/	Good luck from their main page
HP	http://www.hp.com	http://www8.hp.com/us/en/drivers.html
Lenovo	http://www.lenovo.com/us/en/	address too long but this is the link
Sony	http://www.sony.com/	address too long but this is the link
Samsung	http://www.samsung.com/us/	http://www.samsung.com/us/support/downloads
Toshiba	http://www.toshiba.com/tai/	http://www.toshiba.com/tai/support.jsp
Other hardware
ATI (video)	https://www.amd.com/en	https://support.amd.com/en-us/download
AMD (components)	http://www.amd.com/en-us	http://support.amd.com/en-us/download
Brother	http://www.brother-usa.com/	http://www.brother-usa.com/support/
Gigabyte (components)	http://www.gigabyte.us/	address too long but this is the link
Intel (components)	http://www.intel.com/	https://downloadcenter.intel.com/
Konica Minolta	https://www.konicaminolta.com/us-en/index.html	https://www.konicaminolta.com/us-en/support/index.html
NVidia (video)	http://www.nvidia.com/	http://www.nvidia.com/object/support.html
Western Digital	http://www.wdc.com	https://support.wdc.com/
Microsoft	www.microsoft.com	https://support.microsoft.com/en-us See also Windows Updates

Common antivirus manufacturers

Avast	https://www.avast.com/	https://www.avast.com/en-us/total-support
Avira	https://www.avira.com/en/avira-free-antivirus	https://www.avira.com/en/support
AVG	free.avg.com	https://support.avg.com/?l=en_US
Bitdefender	http://www.bitdefender.com/	http://www.bitdefender.com/support/
Kaspersky	http://www.kaspersky.com/	http://usa.kaspersky.com/support/
McAfee	https://www.mcafee.com/consumer	http://home.mcafee.com/root/support.aspx
Norton	http://us.norton.com/	https://support.norton.com/
Panda	http://www.pandasecurity.com	http://www.pandasecurity.com/usa/support/
Symantec (business)	https://www.symantec.com/index.jsp	https://support.symantec.com/en_US.html
Trend Micro	http://www.trendmicro.com/us/index.html	http://www.trendmicro.com/us/about-us/contact/
Vipre	http://www.vipreantivirus.com	http://www.vipreantivirus.com/support.aspx

Other common sites you may want

Adobe	www.adobe.com
Java	www.java.com
MalwareBytes (cleanup utility)	https://www.malwarebytes.org
OpenOffice.org	https://www.openoffice.org/

Intel offers an even more comprehensive list of manufacturers: http://www.intel.com/support/oems.htm