The software that comes preinstalled on Windows PCs is often not the best or (in the case of preloaded trial software) cheapest you could be using.
This is a list of the best free alternatives to common Windows software. Despite my free software advocacy, I have selected the best in field for each category for day-to-day ease of use and of course it has to be free to download and use. I have given a screenshot and some benefits for each.
Right click on the images and click 'View Image' (Firefox) or paste their URL into the address bar (IE, others)
Word Processor
OpenOffice.org Writer

Replaces:
Microsoft Office Word
Benefits:
- Free software
- Looks and feels exactly like Microsoft Word
- Supports .doc, .pdf and many other formats
Download.
Spreadsheet Editor
OpenOffice.org Calc

Replaces:
Microsoft Office Excel
Benefits:
- Free software
- Looks and feels exactly like Microsoft Excel
- Supports .xls and many other formats
Download.
Presentation Editor
OpenOffice.org Impress

Replaces:
Microsoft Office Powerpoint
Benefits:
- Free software
- Looks and feels exactly like Microsoft Powerpoint
- Supports .ppt and many other formats
Download.
Web Browser
Mozilla Firefox

Replaces:
Windows Internet Explorer
Benefits:
- More secure than Internet Explorer
- Fully customisable theme
- Free, powerful plugins like Adblock, Fasterfox, NoScript and IETab
- Excellent support of web standards
- Inline search bar and spell checking
- Free software
Download.
E-Mail Client
Mozilla Thunderbird

Replaces:
Windows Mail / Outlook Express / Microsoft Office Outlook
Benefits:
- Built-in spam filter
- Fully customisable theme
- Free, powerful plugins
- Excellent support of web standards
- Get the features of Outlook for free
- Free software
Download.