There are a few applications that have become so ingrained in my workflow that I consider them to be essentials. One such application is 1Password by Agile Bits, however I've recently run into some trouble with it. You see the program is a password manager which integrates with your browser (Safari, Firefox and Chrome) via an extension. The trouble is that the extension is not able to connect to the application anymore for some reason - I've not tried with Chrome but it seems to be the same with both Safari and Firefox. Let's hope the next release solves the problem; it's annoying to have to work around this issue.
On a related but more social note, I'm trying out a new application for my phone called "Path". The idea seems to be similar to Facebook and Foursquare but the UI is much cleaner and more user friendly. It's also designed to be much more reserved for your inner circle. The designers have limited you to 150 friends for this purpose which, if I remember correctly, is based on a magical number. This number is supposedly the maximum number of people that the average person is really friends with and thinks of often. My circle is significantly smaller than that but I've always been a little more introverted than most others!