A comment to my last entry contains a question about growing butternut squash in San Francisco. This is one of the best winter squashes to grow in California, since it is in a species of squash that is relatively resistant to powdery mildew. When you are looking in a seed catalog, or on a seed packet, look carefully to find the scientific name of the squash variety you are considering. Look for the name "Cucurbita moschata." It may be called butternut, or could have a different name, but it will share the powdery mildew resistance trait.
I don't have space to grow many winter squashes, so don't grow them every year, but if I were looking, I'd start with some seed sources I trust, and see what they carry. I'd look at www.territorialseed.com, www.nicholsgardennursery.com, and www.johnnysseeds.com.
Most butternuts have the typical bottle shape, but there are other shapes. Territorial has a round one called 'Long Island Cheese' and www.abundantlifeseeds.com, which sells only heirloom varieties, carries a round one called 'Kikuzu'. Both of these companies also sell 'Futsu Black', a squat rounded type from Japan.
Another C. moschata is tromboncino squash, one that is eaten most often as a summer squash, when it is very young. It is long and pale green at the stage you eat it, a bit firmer than a zucch.
All of these squashes can be trained up a tall trellis. They may try to twist away from the trellis and so have to be tied to it as they grow, but will usually attach with at least some tendrils. If you intend to grow the winter squash types, you may need to hang the fruits in a soft cloth sling as they ripen, since they will get pretty heavy. Old nylons are often recommended, if you happen to have them, though old tee shirt material should work fine too.
My experience is that the coldest, windiest parts of San Francisco are a challenge for these crops, but in the parts of the City that get more summer sun and in wind-protected garden locations where heat can build up a bit, they can be reasonably productive.
For winter squash to have time to make mature fruits, best to plant in May. I was very late last year getting in tromboncino--not till mid July. Even in the Mission garden where I grew them, this was pushing it, but I started them inside, and then planted them in large bottomless black plastic pots full of potting mix to keep the soil as warm as possible, and got a few fruits before the inevitable fall decline. Don't recommend starting so late though.
You need bees for pollinization of all of these squash. Planting some borage or cerinthe will attract them. Both reseed and can be a bit pesty, but at least they are pretty. And the flowers of the borage are edible, tasting like cucumber, so they can be welcome in salad or floating in iced tea.