How would I market RPGs to a general audience? The same way most everything else is marketed: use a celebrity pitchman. This may sound like a smartass answer, but I'm quite serious. Role-playing is usually associated with hopeless social misfits and computer geeks, hence the negative connotation.
Pretty girl: "Who should I go out with this weekend."
Bob: "I'm a D&D player where I play a seventh level druid."
Chuck: "I'm on the football team where I play quarterback."
Pretty girl: "Oooooh, Chuck (squeal)!"
Now there are several celebrities out there who have heartily admitted to playing and enjoying RPGs for a long time. The three that I can think of off the top of my head are Elijah Wood, Jolene Blaylock, and Vin Diesel. Think about getting Vin Diesel as the spokesperson for WotC. Hell, think about Elijah Wood pitching the LotR RPG. And can you IMAGINE the response a game would get if Jolene Blaylock's picture appeared on the cover of the main rulebook? The unspoken thought would be "If these cool, beautiful people play these games, then I will be more like them if I play, too." In business terms, this is known as shameless pimping, but it works.
Another avenue to get more people into RPGs is to advertise them on tv! This might seem obvious, but when it the last time that any of us saw any commercials for RPGs? Sticking a few commercials in a prime time viewing slot might go a long way to getting the word out to the mass market.
And by all means, we need a game that is going to appeal to EVERYBODY. It should be fun, allow for all sorts of adventures ad character types, have easy rules, and should have a non-gaming reference point that everybody is familiar with. That said, I have absolutely no clue why nobody has come out with a game based on Harry Potter. Think about it; it would be an instant hit and EVERYBODY would want to buy it so they could play Hogwarts students standing shoulder-to-shoulder with Harry, Dumbledore, Mad-Eye Moody & co. as they try to prevent You-Know-Who from regaining his old power. Hell, I'd play it.
Finally, just a word on religious role-playing-games. There is an excellent game out called Holy Lands which will be coming out with it's second edition very soon. Also, in less than a month we will be seeing a d20 game called Testament: Role-Playing in the Biblical Age. From what little I have seen of it, it looks absolutely incredible. Heck, it gives me an uncontrollable urge to go out and smite Philistines!