I've never been a fan of reputation and like features. I feel that they very easily become popularity contests about personality and friends 'liking' their friends because of who they are, rather than the content of a post.
That said, if we are to have such a feature, then the mod that DoN has linked to does look good. My only suggestion would be to ensure that a reason has to be given to explain why a post was 'liked' (assuming it's possible to make giving a reason compulsory - it was unclear from reading the mod whether this can be achieved), and perhaps removing the option to give negative 'dislikes', as it seems better to me to focus on positivity than negativity.