<p>What are the options? How popular are they? Do these IDEs give similar/better functionality compared to visual studio?</p>

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:
http://www.microsoft.com/express/vcsharp/