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\'
Objective-C with Cocoa should be your first, second, and third choices. That being said the learning curve can be steep but half the fun of this business is learning something new.
At my job (Seapine Software) we extensively use C++ with the Qt framework on the Mac and it also seems to work fine. If I were starting out I'd definitely go with Objective-C.