This crazy brony from ponibooru actually took the time to map out every single possible shipping combo for every major character in the show. I can't even begin to imagine how tedious this was.
Can't say I agree with Trixlight though! Twixie is 100% cooler. *EDIT* Apparently it's there!
The html for my ghetto rigging up there is crazy long, so if it doesn't load, try this link!