Definitely trust Melanie W. she knows of what she speaks! Also I don't know if she's listed it but Warakabune on Church & 15th has good ramen. It's a sushi boat place that is fairly inexpensive. They've got several types of udon and several ramens. Beware though... the spicy one... is nose burning.
At the appropriately named: Tanpopo in J- town. If you dont want to commit - get the fried rice which comes with a bowl of the broth in lieu of miso. The broth will make you want to order the ramen as your next course.
I particularly like the ankake ramen they have here. It's shoyu ramen with fresh vegetables in a starchy sauce - tastes a lot better than it sounds. My friends love the karamiso (red spicy bean paste) ramen. Haven't found any other place in SF that makes these varieties.