This page lists variant pronunciations and their standard readings in Mandarin Chinese (Mainland Standard). It does not list characters that have different readings based on different meanings, so characters like 好 are not listed (they do have different readings, but for distinctly different meanings, which can be found in any dictionary). It tells you such useful things as when 薄 is read "báo" and when it's read "bó":

（一）báo（语） 常单用，如“纸很～”。

（二）bó （文） 多用于复音词。 ～弱 稀～

It should be mentioned that this list is NOT exhaustive, it merely lists cases that can be used to check how well students know their character readings.