Free open source software

For Web Browsing
1. Firefox - Been using FF in all its incarnations and it is miles ahead if the OTHER one. It is much faster, lightweight (wont suck 100% of your CPU), simpler, stops annoying popups and has tons of great plug-ins that can make surfing the web a real pleasure.

Email
1. Thunderbird (instead of Microsoft Outlook)
Thunderbird is an email client that has the main features desired in any email client or software for that matter - rich (full) feature set, lightweight, fast, a very good spam filter, and last but not the least protects you from those ridiculous phishing attacks by clearly indicating which emails send you to a bogus website.

Antivirus
1. ClamWin Why pay for Norton or McAfee anymore?
ClamWin is a smart anti-virus software that is fast, easy to manage and unobtrusive (wont eat up your CPU and make it slow) while keep your system free of viruses.

PDFCreator (use instead of Adobe Acrobat)
PDFCreator creates a virtual printer on your computer and if you print a document to this virtual printer from any program, it creates a PDF of that document that can be read on any computer with Acrobat Reader on it. You don't need to fork out money for Adobe Pro or any other utility when this baby does the same ... free !

GnuCash (Replaces Microsoft Money or Quicken)
GnuCash is a slimmed-down version of Microsoft Money and Quicken packages, but it contains all of the features a user wants for managing money. The interface is incredibly simple, but the software has a lot of punch.

Word Processing / Office Suites
1. OpenOffice
Instead of paying for Microsoft Office, give this a try . It includes very nice alternatives for Excel and PowerPoint (and decent replacements for Access, Word and other Office elements)

Photo Editing / Graphics
1. GIMP (instead of Adobe Photoshop)
GIMP is an acronym for GNU Image Manipulation Program. This prog is great at such tasks as photo retouching, image composition and image authoring. It is feature rich, and free ! So now why pay excessive amounts for Photoshop

Video Player
1. Mplayer (instead of Windows Media Player, Quicktime, RealPlayer, etc.)
One player to rule them all! Plays anything under the sun. Use its keyboard shortcuts and you will never use any other player ever ! The most interesting is use of arrow keys to move within the video. The plain MPlayer has no GUI (graphical user interface) and can be a little tricky because of the command line hassle. My recommendation is to go with MPUI.

2. VLC Media Player (Replaces Windows Media Player, Quicktime, RealPlayer, etc.)
Similar to MPlayer, plays all media formats and has a clean, simple interface.