30 can be quite a significant birthday for many women. We all pitched in and bought our daughter an emerald ring - the stone is the birthstone of her first born.
My friend in California - her friends contacted all her friends, far and near, to create a page for a friends memory book. We each made a scrapbook page signifying our friendship with Candi. It was loads of fun to create and very exciting to hear about her reaction to each person's page.
Because its a significant birthday, I tend toward the very personal gift for this one.