I went to Jared to pick out my wife's engagement ring, and ultimately we got our wedding bands there as well. The sales staff is very friendly and professional. They really helped me to pick out a ring, especially since the ring was a surprise and my (then) girlfriend had not told me anything about what she liked or didn't like in a ring. For sizing I devised a scheme: She had another ring that she always wore on her right ring finger. I tried that one on My hand and memorized how far up my finger it would fit. When I went to Jared's I chose a size that matched that spot. However, the only problem that right and left hands are very different - her right ring finger is a size or two bigger because she is right handed! Oh well, the people at Jared's got it sized for her in a jiffy.
If you go, enjoy a free cup of coffee, cocoa or cappuccino while you shop.