Schematron and Relax NG are a bunch that I like a lot for checking structure.
Unfortunatly though, neither of these schemas contain enough information for generating the code.
A way of supporting these would be using them just for validation and not for the actual code generation. But that means you would still need an XSD schema for the code generation.
I agree that XSD schemas tend to be utterly ugly. Using a graphical aidfor designing the schema helps a lot. Here's a bunch:
editix -- freeware
Oxygen -- Personal/Academic version below $50
XmlSpy -- The best. But runs only on windoz. Around $500 I think.