Visual Studio
I've always preferred a minimalist approach to coding. While I transitioned with most people to using an IDE in the early 90s. I soon transitioned back again. I found that when I was writing code I didn't want distractions and invariably both the editor and the build program integrated with IDEs were vastly inferior to those available in specialist tools.
To be specific, how many IDEs would enable you to type say ":1,$ s/([a-z]*) ([a-z])*/\2 \1/" and have every second and first word swapped? I bounced between emacs and vi a bit as to which editor I preferred but while I periodically tried the latest IDEs I always found them woefully inferior. Build commands were similar, I was able to develop a custom preprocessor, integrate source control, or even FTP required files all as part of build scripts using make while IDEs struggled with anything more than a dependency tree. They even had an irritating habit of trying to recompile your code when you just edit the comments, something that's easy to override using specialist tools.
When using windows you don't get much choice except to use an IDE. Microsoft has been pushing Visual Studio for many years - offering it as a free download, bundling it with IronPython, moving DTS and SSRS into it, and generally expecting you to use it everywhere.
Not long ago I upgraded to Visual Studio 2012 and, much to my surprise, I was absolutely blown away. Firstly this version supports both programming and database development whereas the previous BIDS install didn't want to integrate with a C# install. But the quality of the development ecosystem integration is where the latest version really shines. Source control isn't just built in, it's beautifully integrated throughout the program, build servers, automated regression testing, agile style task management, it's all amazingly slick.
So, well done Microsoft. After twenty years of ignoring IDEs, you've released some software which is so good that you've changed how I work.
Incidentally 2013 came out the other day. It's a solid incremental update with the most interesting feature being nice deployment management. Nothing to get excited about but after such a brilliant release in 2012 I had expected Microsoft to release a dud.