747 Junkyard argument
The tornado argument states that evolution is like a tornado moving through a junkyard and assembling a fully-functional 747. This analogy plays off the percieved "randomness" of evolution on the part of the creationists.
The problem with the analogy is that evolution doesn't work in massive jumps like a tornado would. Evolution has no goal; instead, it works with what already exists and modifies it to accomplish new things.