1. Bark or Wood ChipsAmong the most commonly used mulches, bark and wood chips are easily available in bags from garden centers but can also be obtained (sometimes for free) from tree services. Wood chips can be slow to deteriorate, but they can temporarily bind up nitrogen in the soil as they do, which robs nearby plants of needed nutrition. Bark chips can also be toxic to plants if they are too fresh. You can also buy bags of colored wood chip mulches (generally red, brown, and black).
3. Alfalfa Hay or PelletsThis is a more expensive option but a good source of nitrogen for the soil. It is seedless and long-lasting compared to rice straw. Since it is pelletized and bagged, it is easier to transport than bales of straw.
4. Shredded Redwood "Hair"Shredded redwood can be a very attractive mulch, but it's lightweight and can blow around. Also, weed seeds and other debris can get caught in the finely shredded fibers, making it messy.
5. Cocoa Bean HullsThis mulch gained a lot of popularity primarily for its fragrance. It smells like chocolate. The downside is the fragrance doesn't last long, it's expensive, and it's lightweight enough to blow away. It can also be toxic for dogs if they should eat it.
6. Grape Seed Mulch or CompostIf you live anywhere near wine country, you may have easy access to grape seed mulch, which is basically winery waste. It is a really dark (almost black) mulch that is long lasting and will feed the soil as it decomposes. It's not as readily available as other mulches but nurseries and soil suppliers may be able to hook you up. Depending on the source, you may need to screen or filter it before spreading it out to remove bits of vine and other debris.
7. Pine Needles and Other Leaf MulchesIf you have a good source for pine needles, you have a gardener's goldmine. Pine needles make a terrific acidifying mulch. Not only are they free, they're also long lasting and don't compact too much, making them a good choice for mulching paths in vegetable beds. Again, you may need to screen it first to filter out other debris. Other leaves can be used as well--oak leaf mulch is another good option, although it is not as acidifying as pine needles.
For a more complete discussion of mulches, check out my book, California Month-by-Month Gardening.