I would try a google search, too. I have had success by using the google picture search and then browse through the pictures linked to words like "SC4 diagonal building". By this, you can easily see, what buildings are there. In case you find some nice buildings but cannot find the name or the downloadlink, you can ask here or on the other SC4 site "simtropolis" in threads called "can't find it? ask here...".
To give you at least something solid now: there were quite a view diagonals on the simcity polska site. You can find them now on simtropolis.com (unfortunately the site had some issues, so you might have to wait for them to be back online). The houses look like these:

I really like
these houses. Unfortunately, they are not meant to be plopped next to a diagonal road, but they give a city a nice diagonal look.
