I read something about an Eclipse plug-in but that seems to be "out of print".
Yeah. Unfortunately Brucey kinda stopped working on it, for some reason. Us Linux users are pretty much in the same sorry state of affair. I would have bought Blide, but contrary to claims made by its author, it doesn't work on mono (like I told him).Still, if you can live with the limitations of older versions of Eclipse, the Eclipse plug-in is probably your best bet - the Community Edition IDE, while much better than the official IDE, still has quite a while to go before it can hope to match Eclipse. I don't even think it would be possible, considering the limitations of MaxGUI (but feel free to prove me wrong).
I was working on a plug-in for X-Develop but it seems like support for X-Develop has all but disappeared and the much anticipated support for compilers that aren't Java or .Net isn't likely to materialize any time soon. Sorry.