The following products have been officially discontinued by Canon, so if you find them in stock anywhere, the time is now.
The 580EX II is highly recommended, I rent a lot of them and they've been bulletproof.
Everything on this list has been replaced by newer, and more expensive versions. The EF 24 f/2.8 IS, EF 28 f/2.8 IS and EF 24-70 f/2.8L II have not begun shipping yet, and we're hearing July 2012 at the earliest. The Speedlite 600EX-RT has begun shipping in pretty good quantities.