Not even close to true. He doesn't own ABC, CBS, or NBC. He does own Fox, one of four major networks. On cable, you have Fox News owned by Murdoch (very Republican-oriented, granted), CNN owned by Ted Turner (debatable), but the rest of the news channels aren't close to right-leaning in general. For newspapers, he owns the WSJ, which is the only prominent right-leaning paper, with the Washington Post and New York Times being the two most prominent newspapers in the country. They also happen to be *extremely* left.
So your big Republican conspiracy is 1 out of 4 major networks, one or two major cable news channels, and one major newspaper. That's a lot more than those that are clearly left-leaning. The network news tends to skew left, as do newspapers in major cities.
Correct, Murdoch doesn't own the "most of the mainstream media".
He does own a larger percentage than just about any other single entity, (the New York Post too) but he doesn't control the whole picture.
ABC is owned by Disney, CBS is owned by Viacom / National Amusements, Inc., NBC is owned by GE
You could try and say that Disney, Viacom and GE are totally Republican because they're big business, but then you could come back and say they all love Obama so that makes them Democrats.
Fox is about the only one that with a very obvious news slant, typically coming from pundits like Bill O'Reilly or Sean Hannity, but they don't speak for the whole corporation.
The whole left/right slant thing is COMPLETE BULLSHIT for most news organizations.
The truth is, they're all about ratings and making money, regardless of left or right.
As for newspapers, isn't Google News the most popular? :)
I just watch Jon Stewart anyways, he must be neutral. Oh shit, Comedy Central is owned by Viacom so there goes that!