Boston Globe had this great article on How movie taglines are born. This was way back in 2004. Here's an extract from it to get you tempted:
In-house copywriters at specialized poster design firms (virtually all in Los Angeles) may collaborate with freelancers and the studios' own marketing departments to churn out as many as 1,000 tagline ideas for a given film. Writers are shown a rough cut of the film, a script, or even just synopsis. Turnaround times range from a year to a few days.
"I usually sit down and if it's there, it's there. It's not the kind of thing, at least for me, where you sit and stare at your computer screen," says Mike Kaiser of the design firm Concept Arts, who has been writing copy for 25 years. (His father was a copywriter, and so is his son.) Kaiser will jump around a thesaurus or Bartlett's Familiar Quotations, looking for phrases he can "spin or twist." His most famous line -- "The first casualty of war is innocence," for "Platoon" -- grew from Senator Hiram Johnson's 1917 assertion "The first casualty of war is the truth."
Stuart Bauer of the marketing firm BLT & Associates pored over countless radio stations' listener-favorites lists from the 1960s and `70s in search of tagline fodder for last year's "School of Rock." He ultimately pinched a line from Pink Floyd's "The Wall": "We don't need no education." Bauer's line for "Sylvia" ("Life was too small to contain her . . .") alludes to the title of Sylvia Plath's most famous work, "The Bell Jar." For "Scooby-Doo" ("Be Afraid. Be Kind of Afraid.") he reworked the seminal tagline for The Fly ("Be Afraid. Be Very Afraid.")
For the whole nine yards, go here.