I'm bookmarking this thread, too -- your ideas are so creative! I will definitely be using the entertainment center one and the island desk. :) I'm kind of in the same boat as @kristinemancuso. I LOVE to construct the buildings themselves, but I find myself using the same wall coverings and furnishings and color schemes over and over.
I don't know if this would be new or useful for anyone, but I did discover recently that you can sandwich a kitchen counter between two walls and then use solid fencing on the front wall to make it a half-wall which gives you sort of a 'built in' look and a shelf that allows you to place some of the larger clutter/sculpture/plant items that won't fit on the regular wall shelves. It's only decorative, though -- sims can't use anything that's on the shelf because they see a 'wall' between them and the object -- so it's no good as a desk, etc. Something like this:
http://i.imgur.com/iXem2kM.jpg
Now, if only there was an actual half wall that we could put any wall covering we want on! :)