AP and Reuters seem to be alright in my experience, as do some foreign sources (BBC). AllSides.com provides media bias ratings which pass my sanity filter, although I won't claim to know how trustworthy a source they are.
I don't know how I feel about allsides.com bias ratings. The Economist and The New York Times (news only) appear in the left-leaning column. The New York Times (opinion) appears in the solid left column. Given The Economist's solid advocacy for business and free trade, and Douthat and Brooks and Stephens as NYT opinion writers, I'm positive this isn't even slightly accurate.
Treating allsides.com as propaganda, as another commenter here has advocated, I'd have to say that allsides.com is shifted everything left one column, or maybe more.
I don't know enough about individual publications to say whether I agree that their ratings are off, but I do like how allsides allows you to vote on whether you agree with their ratings[1] -- and I encourage you to. At least out of their site visitors, there seems to be a decent degree of agreement. I think what they're trying to do is admirable and it's an extra bit of legitimacy that they're willing to admit they're not perfect. If there's a better source for exploring media bias out there, I'm not aware of it.
I'm seeking a website for politics similar to what Patheos does for religion and non-religious perspectives. All the biases are present, but they are more clearly delineated and categorized in different "channels".
Treating allsides.com as propaganda, as another commenter here has advocated, I'd have to say that allsides.com is shifted everything left one column, or maybe more.