Few of my favorites:

Most software today is very much like an Egyptian pyramid with millions of bricks piled on top of each other, with no structural integrity, but just done by brute force and thousands of slaves. [Alan Kay]

Hofstadter's Law: It always takes longer than you expect, even when you take into account Hofstadter's Law.

Debugging is twice as hard as writing the code in the first place. Therefore, if you write the code as cleverly as possible, you are, by definition, not smart enough to debug it. [Brian W. Kernighan]

The primary duty of an exception handler is to get the error out of the lap of the programmer and into the surprised face of the user. Provided you keep this cardinal rule in mind, you can't go far wrong.[Verity Stob]

Programming can be fun, so can cryptography; however they should not be combined.[Kreitzberg and Shneiderman]

The best performance improvement is the transition from the nonworking state to the working state [John Ousterhout]

I have always wished that my computer would be as easy to use as my telephone. My wish has come true. I no longer know how to use my telephone. [Bjarne Stroustrup]

Theory is when you know something, but it doesn't work. Practice is when something works, but you don't know why.
Programmers combine theory and practice: Nothing works and they don't know why. [Anonymous]

For every complex problem there is an answer that is clear, simple, and wrong. [H L Mencken]

One of the main causes of the fall of the Roman Empire was that, lacking zero, they had no way to indicate successful termination of their C programs. [Robert Firth]

...well over half of the time you spend working on a project (on the order of 70 percent) is spent thinking, and no tool, no matter how advanced, can think for you. Consequently, even if a tool did everything except the thinking for you -- if it wrote 100 percent of the code, wrote 100 percent of the documentation, did 100 percent of the testing, burned the CD-ROMs, put them in boxes, and mailed them to your customers -- the best you could hope for would be a 30 percent improvement in productivity. In order to do better than that, you have to change the way you think. [Fred Brook]

Never attribute to malice that which is adequately explained by stupidity. [Hanlon's razor]

Sufficiently advanced incompetence is indistinguishable from malice. [Anon]

For more, try this, this or this.