the great leveller at weddings is the variety of ages, incomes, and fashion sense of the guests of both sexes. If the wedding is formal, then a suit is mandatory, but co-ordinated casual jacket and trousers are OK. If you don't want to wear a tie, wear a shirt that doesn't reuquire one - an open-necked shirt looks like you haven't bothered, so go for designer casual, or standard with tie. For the evening, an open necked shirt is fine, maybe with some light casual trousers and casual shoes. If all else fails, remember, people will be checking the bride and groom, and unless you are dressed as a Japanese general, you are unlikely to stand out as a fashion disaster. Hope you enjoy yourself.