"What's the simplest thing that could possibly work?" This was the theme of an online article about software development. A great question to ask frequently.
"One characteristic of a user-friendly system is that it does what the user wants." Great definition. Simple but true.
"The upset over a missed deadline goes away much faster than the terrible taste of a bad product."
And here is a quote that I found as a SlashDot signature. It was attributed to Richard Feynman.
"Physics is to math as sex is to masturbation." This one was particularly interesting to me because I first saw it just after I had read a chapter on math and its relationship to physics in the book "The Soul of Science".