I have some pretty heavy functions that I've placed in my model class because I need them to be accessible through many interfaces on the site. But how can I call these functions from my controller class? Here's the best thing I can come up with:

public function myFunction()
{
$model_class = str_replace(get_class($this), "_Controller", "");
return DataObject::get_by_id($model_class,$this->ID)->myFunction($arg1, $arg2);
}

Ordinarily, I'd just call the function normally from the template, but the controller is used to parse data out of the url first, and then pass it to the model with $arg1, $arg2...

Does it have to be that ugly?

You can access a model method through the $this object in the controller. For me the following code works:

class Page extends SiteTree {
	public function MyModelMethod() {
		return $something;
	} 
}

class Page_Controller extends ContentController {
	public function MyControllerMethod() {
		$v = $this->MyModelMethod();
	}
}