What are the options? How popular are they? Do these IDEs give similar/better functionality compared to visual studio?
Yes - you can try using SharpDevelop:
http://www.icsharpcode.net/OpenSource/SD/
Or you can just use notepad, or notepad++
http://notepad-plus.sourceforge.net/
Then compile on the command line.
Edit: If you're looking for a free solution - try Visual Studio C# Express Edition:
Check out the mono project. http://www.mono-project.com/
It's the '.NET for linux' project.
They also have an ide based on eclipse as part of the whole thing. Never used it before but I've used eclipse for java and some php work, and eclipse is pretty good
Edit: the ide is called MonoDevelop. Seen at http://www.monodevelop.com/
You do
SharpDevelop - It doesn't really stand up to Visual Studio. Thou I found it to be useful at times since it has support for Visual Basic. And at times I could load solutions for projects that were not installed on my VS. But the really USEFUL features that I found were : Conversion between C# <-> VB Code, PInvoke, and Regex Expressions. Oh and lets not forget support for Boo :D. there is also Borland C# Builder AFAIK. Only saw a tutorial long ago written by someone who has used it.
MonoDevelop - link text This is based on SharpDevelop 0.9 if I remember it correctly. I have to say I only used it once to see if I can work with threads in Linux just like in Windows.
That's about all I remember, I'm pretty sure there are at least one more IDE but I don't remember it now :). Also they don't really match up to VS + Resharper :) or + CodeRush.
Plus you have Visual Studio Express so unless you have to work on Linux or have some projects that you think you could try opening in #D there isn't much out there. MonoDevelop is starting to come along try keeping an eye out for it.
I found this refrences also X-Code
The vast majority of .net developers use Visual Studio, but there are a couple of alternatives.
Visual Studio Express Editions are free and give you a cut down version of Visual Studio which you can use with a single language, i.e. VB or C# or C++.
SharpDevelop is probably the best free alternative to Visual Studio. It's open source and has features like a form designer. It supports the full range of .net languages (including IronPython, F# and Boo). It also has features not found in Visual Studio, like the ability to translate between C# and VB.net. You can even mix different languages in the same project.
MonoDevelop is also free and open source. It only runs on Linux though, so it's not a viable alternative for most .net developers.
The .net compilers are all free and included with the SDK. This means you can always use any text editor and compile from the command line. This would be pretty painful to do with anything other than a really simple program!