I read various threads on slowtrav.com about attending a wedding in Italy and what it is "proper" and what is not. Things are evolving and differ between regions but here is my advice:
OUTFIT: Although it is becoming more popular to get married in the afternoon with evening reception, morning ceremonies are still very popular. I would never wear a black or white dress at a morning wedding, nor in the evening, unless specifically requested. You may ask and people may do it, but it is considered "tacky".
GIFT: Wedding lists ("Lista nozze" ) are quite popular and they are the easiest way to please the bride and groom without worrying about what you can get them. The amount of money that you spend is totally up to you. There is no fashion and there is no link to what the wedding reception costs at all. If you are travelling from abroad and attending an Italian wedding, a token from your Country may be the best idea. Consider that your Italian friends will know that you are committing quite a bit of money to attend the wedding in terms of travel arrangements, so they won't expect you to go OTT - unless you can afford it!
TOASTS: Italian wedding receptions do not evolve around a specific scheme, like in England where the speeches have a specific format and have to be of a certain length. There are no such a thing like speeches and people just sit and chat all the time. If there are lively groups of friends or cousins, people may end up cheering the bride and groom or asking for a "bacio" (kiss) towards the end of the meal, but nothing formal and always very spontaneous.