If coding in Java is an option, I would highly recommend SWT (http://www.eclipse.org/swt/). It's the toolkit that was used to build Eclipse, and it has a very 'native' look & feel (click the link for examples).
Plus, Java itself is cross-platform. Might be just what you're looking for.
Java GUI's always seem just a little bit unresponsive, an irritating latency with every small move you make. This is my biggest complaint with eclipse and every other java app I've ever used.
Plus, Java itself is cross-platform. Might be just what you're looking for.