Believe it or not, there are many ways to express surprise or disbelief without using the phrase "believe it or not". Some possible synonyms include "unbelievable", "incredible", "astonishing", "surprising", and "shocking". Other options might include "mind-blowing", "unimaginable", "breathtaking", "jaw-dropping", or "fantastic". Depending on the context, phrases like "you won't believe this", "I can hardly believe it myself", or "this is hard to fathom" might also be appropriate. Whatever term is used, the goal is to communicate a sense of wonder, disbelief, or shock to the listener or reader.