I\'m planing to buy a Mac. I would like to be able to develop GUI applications for Mac as well. Currently I develop in C# using VisualStudio as IDE. I also know Java and I\'
There really is only one choice and that's Objective-C and XCode, anything else and you'll be running into problems and/or limitations.
As some have mentioned Python is one suggestion but what GUI toolkit to use? Then packaging becomes a problem.
Mono is OK but still a little buggy (and slooooow) on Mac's.
I haven't tried Java but the Apple port of the Java VM has just beed deprecated, make of that what you will.
XCode is very very good and integrates nicely with Mac/iPhone/iPad etc. but Obj-C takes a while to learn coming from a C#/Java background, plus XCode forces you to use MVC patterns in everything which again can be a culture shock.
I would say go with Obj-C and XCode and learn something new.