For #WindowsPhone's birthday, I added support for arbitrary numbers of columns via a config file and here's an example three-column layout I set up. Ran out of apps for the bottom-right so I just put three small RetiledSearch tiles there. You can now also change tile spacing, if you want. I may need to change the text size though, unless it's fine.
It's also start.config, if you want to know the file it's in.