Who has the highest official Dragon Ball Z power level? I remember Captain Ginyu exclaiming that Goku had a power level of 180,000 in the Ginyu Force arc, but I don't recall a higher scouter being shown/read aloud in any other episode/movie of DBZ (I'm not including Frieza's 1 million bluff).

Does anyone have more information on this from a credible source? If official data is available, I would also want to know the power levels of a regular Super Saiyan, SS2 and SS3 as well.
I'm not sure how credible you consider the Dragon Ball Wiki, but they have compiled a list of power levels of most characters mentioned throughout the series, including GT.

The highest power levels in that list would be the old Supreme Kai's at at most 120 billion, while the next largest power level would be Gogeta SSJ4 at 25 billion.

See here for a more exhaustive list.