I tend to use "oh my gosh" or "oh dear", but there are as many ways to express surprise as there are people! If someone scares me and I want to express negative surprise, I often say "sheesh, you scared me!" It depends on the people you are talking to. There is a chance that if the person is religious, they will be offended by "oh my god", mostly because it feels insincere. If I am expressing sympathy towards another person, I say "Aw, man, that's awful," but only in very informal situations. I hope that helps! ^_^
Emily