Mono has gained serious traction the last few years. I've personally been using it along side .Net and am loving it. You could develop in Windows with the Free/Express versions of Visual Studio etc. and deploy binaries to Linux. You could also use monodevelop (http://monodevelop.com) in Linux or OSX. There are C# plugins for Eclipse and IntelliJ as well.
> There are C# plugins for Eclipse and IntelliJ as well
No, there aren't. And MonoDevelop has gotten better, Xamarin is doing a good job, but it's still a far cry from IntelliJ IDEA. If you want to target Mono, spare yourself the effort and just use Visual Studio.
Relevant: http://www.mono-project.com/Companies_Using_Mono https://servicestack.net/features http://stackoverflow.com/questions/18450/is-mono-ready-for-p...