I'm really lazy. I develop for Linux (could even do this on Windows with GTK for WIndows). I then have a series of hacks to auto-hildonize my application.

So I use Glade as an interface builder (I haven't tried to use it with Hildon widgets, thats what my auto-hildonization is for).

GTK has VBox, HBox and Table (which has span support) for being able to seperate out the screen into various parts. I use these heavily in my apps.

Depending on what I do, I regularly use the PyGTK Tutorial, the PyGTK Reference, PyMaemo APIs Reference, Diablo and Fremantle API Reference for areas PyMaemo hasn't documented clearly enough.

Other than that, nothing too special. Except for maybe my auto-hildonization, I personally think Dialcentral code is pretty clean to use as an example (I know, unbiased aren't I?). ejpi is a bit smaller of a project which might make it more approachable but I haven't pulled all of my improvements I made to Dialcentral into ejpi yet.