Swooshable is the best online collection of LEGO techniques, instructions and tools.
Lego Window 1 x 4 x 6 Revolving Door 7894 Glass Pane | eBay
Verzahnte Schrägsteine | Tobias Buckdahn
Doppel-U-Oval | Tobias Buckdahn
This is not my own technique, but Clonemaker829 asked how it was done and I couldn't find a photo that explained how to do it, so I thought I would upload this photo for him and others who don't know the technique. -Tristan