The three examples that first springs to mind are slavery, pedophilia, and the holocaust.
If "god" is all powerful and all good, and knows everything before hand, then "god" would not allow such things to happen.
However if you drop any one of those three, it's concievable that these things could happen inspite of a "god".
I know that many people say these things are part of "god's" bigger plan, and meant to teach us a lesson that we just don't understand, but frankly I find that to be disingenuous.
If people want to claim that things such as stem cell research are wrong in god's view, or that gay marrage should be outlawed, or that people should not read Harry Potter because these things offend "god", then we should be able to understand "god" on the big things as well (like slavery, which IMO is just about the worst thing one human, or group of humans, can do to another human, or group of humans).
IMO either "god" knew these things would happen, and as a "good" person wanted to stop them but was powerless
or "god" knew, and how the power, but did not give a shit
or "god" had the power, and wanted to, but did not know in advance (either that it would happen, or how to stop it)
or some variation of these three to different degrees.