Our C++/QT desktop application for Mac, Windows and Linux needs an installer. I\'d rather we have a single installer for all three platforms. I do know it\'s a bit tricky, I
The link that Kyle mentions is pretty comprehensive, but I wanted to provide a bit more of information about InstallBuilder for Qt (Disclaimer, I am one of the developers) since most of the cross platform installation programs referenced there are Java-based. This requires bundling a JRE, etc. and adds a significant overhead that is not required with a Qt-based installer, like ours. It is able to generate wizard-like executable installers for all platforms from a single project file as well as native packages such as DEB and RPM. If you ship your software in DVDs, you can create a single multi-platform DVD that shares data across platforms but still have native launchers.
Having said this, since your application is Desktop-oriented, for the particular case of OS X if it does not require complex installation you may be better off creating a .app file and package it inside a DMG. Users can then drag the file directly to the Applications folder.
Finally, I wanted to mention that InstallBuilder is commercial, but we offer free licenses for open source projects and discounts for small development firms.