Useful Tools

Adobe Acrobat Reader - required if you want to be able to view PDF files. A must get.
Winzip - The best utility for unzipping files. Goes far beyond the built in support of Windows XP.
Winamp - Probably the best MP3 player around.
ACDSee - The best picture viewer/organizer.
Trillian - Chat program that puts AIM, ICQ, Yahoo Messenger, and MSN Messenger all into one program.

Software Update Sites

WindowsUpdate - The most important one around. Everyone with any version of Windows should be visiting this often.
OfficeUpdate - For users with any version of Microsoft Office, inlcuding: Word, Excel, Access, Powerpoint.

Online Dictionaries, Thesauri , etc.

Merriam-Webster - Very nice and not laden with a lot of advertising.
Microsoft Encarta Online - Lots of links to other Encarta content.
BabelFish - Incredibly useful online translation site. Translate just about anything.

Virus Information Pages

AVG Anti-Virus - Excellent Anti-Virus software. They also have a virus information page.
Symantec Security Response - One of the best places to get information about computer Viruses.
Trend Micro - Good database of Virus information.
McAfee - is another good source.

Technology News and Information

CNET Tech News - One of the best.
CNN Tech - has a lot of really good content as well.
CNET Hardware reviews - really trustable source for your technology purchase decisions

Interesting Tools and Software

Flash player - Many web pages use this for animated graphics.
Skype - Free telephone on the Internet
Google Earth - A amazing atlas of the whole planet made from high resolution satellite pictures.