I am a huge fan of using software that saves time. For example, I have talked in the past about:
When I glanced at my TextExpander stats the other day, I was reminded of how much of a time-saver such tools can be, as it showed that TextExpander has saved me about a half hour in the few months since I have installed it:

TextExpander does this through expanding text shortcuts, such as replacing my shortcut of “pppc” with “Pocket PC”. It also does this through catching my spelling errors for the 100 or so commonly misspelled words that are in its “dictionary” (which I can customize).
Another huge time-saver for me on the Mac is QuickSilver. It is one of the most powerful little utilities around for launching apps and manipulating text within apps (you can use it to send emails on the fly, for example). I use it mostly for launching apps, and it saves me a ton of time just in that respect, and it keeps me from having to the mouse so much. Great app. My Keen PDA site provides an introduction on how to use QuickSilver and TextExpander via its Time-Saving Mac Software article. TextExpander is pretty straightforward and easy-to-use, but if you really want to take advantage of all the power of QuickSilver you owe it to yourself to search the archives of 43folders and Lifehacker: both sites have several articles that go pretty deep into the innards of this fine tool.
To my knowledged, QuickSilver does not have a true counterpart in the Windows world, although Launchy is good at handling launching. One thing good for Launchy is that new modules are being added to it all the time, so it could become the Windows equivalent of QuickSilver one day, I suppose. If you are interested in Launchy, you might want to head over to Lifehacker and search their archives on it: they have a number of useful posts related to it.
A neat utility that I wish I had known about before I retired is Anagram. This neat application will take contact information from just about any place that it is “buried” and transfer it, in the right format, to your Outlook Contacts list. So, for example, if you got an email from me that had the following contact info in it at the bottom of the email, you could select it and have Anagram transfer it to your Outlook Contacts data:

A slick app. I do not really have any use for it now that I am retired, but if you have a lot of contact info to go through, this could be a real time-saver for you.
What are your favorite time-saving apps?