VS2010 - C#, C++, C, VB
Eclipse - Java, php (for at work)
NotePad++ (sublimetext2 on my flash drive) - Everything
IDLE - Python
Emacs - Everything when on Linux (including the best language ever...brain****)
ideone.com occasionally as well.
It depends what I'm programming, and what language I'm programming in.
Eclipse - Java
Microsoft Visual C# 2010 Express - C#
Microsoft Visual C++ 2010 Express - C++
Microsoft Visual Basic 2010 Express - VB.NET