There are a number of different apps that I use constantly. This is an incomplete list.
iTerm is my terminal application of choice. I use a terminal almost every single day for much of the day. While I think the built-in Mac OS X Terminal app is an excellent application, iTerm is just a little bit better.
Sparrow has become my mail client of choice. In a nutshell, Sparrow takes some of the excellent paradigm decisions from Gmail and applies those along with other great and innovative features to the desktop email experience.
First off, no web browser is perfect. All have their issues and these issues change with new releases. I generally end up using Safari the most, at least for my general browsing. My second most often used browser would be Google Chrome. These days I basically run my normal browsing in Safari and then some of my sharing (blogging, Tumblr, Google+) in Chrome. Last year I was using Firefox most of the time but it has fallen out of favor for my constant use.
On the subject of web browsers, what in the world is going on with Firefox releases? I think they must be trying to catch their version number up with Internet Explorer so the non-technical user will not think IE is better because it has a higher version number. At the recent rate, we should be hitting Firefox 30 sometime next year. It is hard not to notice that after Firefox 8, everything slowed back down to a normal rate.
There’s no clear winner in this category. I have used VMware Fusion for the longest of the available products on the Mac. It is a great product and ties in well if you are working with larger VMware infrastructure. The fastest and best-integrated option is Parallels Desktop 7 for Mac. I tested out the trial version and was very impressed. It was a nice touch to have a special install of a Chrome OS which is essentially what a Chromebook comes with as its operating system. The other offering in this space is VirtualBox. Of the three, VirtualBox may have the best value since it is free. It also has the easiest way to run headless. It also has the advantage of running on many open source operating systems such as FreeBSD.