Artima referred (via Martin Fowler) to Dan Pritchett's excellent blog Adding Simplicity. Dan is an eBay architect and covers the scalability and reliability issues of distributed web-based systems.
The title of the blog comes from the notion that a great design is "not when there is nothing left to add, but when there is nothing left to take away". Adding simplicity is counter-intuitive; the idea that one has to work at "adding" simplicity. Ira Glass has a great series of videos. Nominally on "storytelling" they are really concerned with how one becomes good at a craft. One big point is the need to throw stuff away. He says something like "anytime you hear a good song or radio play, it's the result of ruthless hacking, trimming, and removing". Things that are good are good because the bad stuff has been taken out. Duh. Yet creative people (and software architects would include themselves here) like to believe that ideas and creativity are a good thing; inspiration shouldn't be tampered with. I certainly see this in software systems where designers get carried away with the "beauty" of their creations over, say, its usefulness to the task at hand.
For software architecture, the key aspect of simplicity is its target. The clients of an architecture are testers, developers (who fix, extend, port, and scale), users, and administrators. Making something more complicated (such as requiring all transactions be idempotent) actually makes things simpler for the people running the production systems.