A free, portable, fast and simple C/C++ IDE
A new and improved fork of Bloodshed Dev-C++
A free IDE for C#, VB.NET, & Boo projects on Microsoft's .NET platform
SharpDevelop is the open-source IDE for the .NET platform. Write applications in languages including C#, VB.NET, F#, IronPython and IronRuby, as well as target rich and reach: Windows Forms or WPF, as well as ASP.NET MVC and WCF. It starts from USB drives, supports read-only projects, comes with integrated unit and performance testing tools, Git, NuGet and a lot more features that make you productive as a developer.
Bluefish is a powerful editor for experienced web designers and programmers. Bluefish supports many programming and markup languages, but it focuses on editing dynamic and interactive websites.
Geany is a small and lightweight integrated development environment. Basic features are syntax highlighting, code completion, code folding, call tips, many supported filetypes.