Windows:
Visual Studio 2005/2010 - Best IDE for Windows. (well, not free - but I use in office only)
Notepad++ : For editing everything.
WAMP - for webdev things.
In Unix :
VIM - for editing everything.
GDB - for debugging.
A lot has changed since this post.
Picked up Spring, prefer
STS (Eclipse) over IntelliJ.
For databases, there's a light IDE -
SqlDBX - one of the best I have used for db. (SqlDeveloper is slow, pgAdmin is okayish)
Sublime has replaced Notepad++ for me.
VSCode is my go to IDE, for anything other than
Java.
Though I am a backend dev, due to some circumstance, responsibility of maintaining some iOS code came on me.
Can't say I am fan of
Xcode, but that's the only option and so getting used to that, learning basics of
Swift.
Was trying to create a small app for personal use, gave a try to
Flutter - though I didn't complete the app, I liked the framework and also the language
Dart.
Android Studio is also decent tool, and being familiar with Eclipse helps.
Trying to join the ML bandwagon, started with the Andrew Ng course - got a bit hands on try on
Octave.
Now trying out
Python libraries, in
Google Colab.
Things haven't changed -
VIM : I still use it and prefer over gui tool.