I'm with the pedants on this one, in that I'd argue the prologue is inseparable from the novel, and the first line would be either be:

"(Supplied by a late consumptive usher..."

or:

"The pale Usher-threadbare in coat, heart, body, and brain; I see him now."

But straight fire either way. And, when it comes down to it, that "Call me Ishmael" is considered so consistently as the novel's opening line makes it the opening line. A testament to its power :-)