Diagram Designer.  Need to draw diagrams like flow charts?  Or layout plans?  Diagram Designer is very simple to use, which is something you often need due to lack of time.
http://meesoft.logicnet.dk/diagramdesigner/

Gammadyne Mailer.  A commercial program for managing email lists and doing email broadcasts (NOT for spamming!).  The power of the program will become clear as you use it.  It is written by someone who knows email marketing well and improves the program continuously to keep up to date with global changes in email marketing.  It is indispensible for anyone wanting to send out newsletters etc.
http://www.gammadyne.com/

MYOB.  One of the simplest accounting packages that ever existed.  Most programs calling themselves 'accounts' are either just a simple cashbook system or are advanced and complex systems.  MYOB was the first to bring that complexity down to simplicity, yet retain the full functionality of double-entry accounts.  It contains every accounting function you would need to run a small to medium business.
http://www.myob.com/

PDFcreator.  PDFs are one of the most popular and convenient methods of sending documents to others.  You could buy the full official PDF editor for over a hundred pounds, or simply use PDFcreator - it creates a 'virtual printer' on your pc.  From almost any program that allows you to select printer before printing, you can instantly 'print' the document to a PDF on your drive.  Does perform well with most text and graphics, but often has problems printing direct web page content.  Web page content is always best printed from a proper web editor (see the Web Design section).
http://www.pdfforge.org/products/pdfcreator/

Foxit PDFReader.  While Acrobat is the usual choice and often comes ready installed on computers, Foxit is more lightweight and faster.
http://www.foxitsoftware.com/

602 Pro LanSuite.  This is a full Web Server suite, but with unique differences - it also is an email server and faxing server.  It can handle the collection of multiple email accounts, and route them automatically to internal Lan recipients (has built in AntiVirus option too).  Clients on a Lan have their own special accounts which lets them email each other without the emails going beyond the Lan.  As a Fax server it not only can receive faxes, route them and print them, but any client can send faxes out by simply sending the fax as an email attachment to the server.  A modem is required for fax receipt and transmission.  All this couples with a standard secure web server too.  As of writing, the program is free for up to 5 users - this enables you to try the program out and if you need more users you can buy a license that suits you.
http://www.software602.com/products/ls/