What are the inspirational resources for building with Duplo?
LEGO does have some interesting and inspirational videos and ideas on their DUPLO website: http://duplo.lego.com/en-us/videos/

One issue with DUPLO is that it is mainly considered as LEGO for babies so all the ideas you will get on LEGO's website will be geared towards small children. However there are adult LEGO fans who also use DUPLO in their creations. Some simply incorporate DUPLO as a support-system for larger LEGO dioramas (like for building up a hill) - a method also used by LEGO's own model builders.

There are also a few adult LEGO fans who use DUPLO for building wonderful creations. One of my favorites is this LEGO DUPLO castle: http://www.flickr.com/photos/joachim_s_mueller/350719605/
Based on it, I also built a DUPLO castle myself: http://www.flickr.com/photos/akunthita/sets/72157617926473583/

In general, flickr.com is a good place to look for DUPLO creations, but again; remember that most will be geared towards small children, so you will have to comb through a lot of rainbow colored towers before you find a really good LEGO DUPLO creation.

Here is an article on how DUPLO and LEGO are compatible and can be used together: http://thebrickblogger.com/2010/12/lego-duplo/