What are the IDE's or development tools best suited for projects involving Objective C, C and C++? Is there a common IDE which would support all the three languages.
If you are using Objective-C for macos or iphone apps it seems there is no way around Xcode from Apple. Xcode has many tools like an Iphone emulator and a profiler for Iphone and macos applications.
For c and c++ I personally would use Eclipse
For Objective-C (on the Mac) it's Xcode, which comes with Mac OS X. It's on the installation DVD. The latest version can be downloaded, for free, from the Apple Developer Connection site.
Xcode, KDevelop, Cocoatron, GNUStep
If Objective-C is your main goal, and you have access to a mac, Xcode is your best bet.
If you aren't going with XCode, I would suggest without hesitation using EMACS. I just picked it up with help from the Peepcode screencast, and I haven't looked back. Even using Visual Studio at work I've now switched to Emacs for every language besides C# (i.e. Javascript, HTML, CSS, Ruby, etc...). It's a bottomless pit of features, in a good and bad way.
Xcode is really the only way to go. If you are crazy-bad-ass and try to use GNUstep and Project Center, you may run into lots of bugs and fail.
For Objective-C you really want to be using a Mac so you can take advantage of the Cocoa, although I have heard good things about using The Cocotron so you can develop cross-platform using Objective-C.
As an IDE I'd either use Xcode or Textmate.
I find Textmate better for if I'm just hacking on some code - I prefer its colour schemes and being able to define and use my own snippets and macros. Also it has support for lots more languages than XCode but it isn't as fully featured.
Also here is a little article about porting Objective-C to Windows using The Cocotron Cocoa With Love