There are many types of weddings and in accordance to those you can select a dress from your wardrobe. For an informal Daytime a women can wear a short dress or a suit and for an informal evening, cocktail dress can be your right choice. Similar dressing up for a semi-formal daytime and semi-formal evening would do. But for a formal daytime you should consider accompanying gloves and hat with short dress or suit and for formal evening or black tie long dress or dressy short cocktail dress, even beaded would look just perfect. For an ultra-formal or white tie, a long gown, with a fur scarf, diamonds and accessories is perfect.
There are other few things that you should take care about while selecting a dress beside above and those are, while going for a wedding don't ever wear a white, because it competes with the bride, there are plenty of other colors around you just need to search them. Don't wear black or sequins during daytime looks very inauspicious. Once I told about the bride that doesn't mean you even need to bother about bridesmaids or mothers, you can't coordinate with everyone in the wedding party. Wear something feminine and appropriate, out of respects for your hosts. Overtly sexy clothing, club wear doesn't belong at a wedding.
There few more things that feel I like addressing as if not considered may put all your efforts in vain, like don't wear top of arm gloves with anything but sleeveless or strapless gowns. Do take off gloves to eat or drink. Use good judgment if the invitation does not specify the formality of the event. A pastel suit or soft floral dress for daytime or a little black dress for evening will take you almost anywhere.
You can get your choice of daytime dresses or cocktail dresses here