• Compost - adds vital nutrients, microbes, and makes for great soil texture. Make your own compost or purchase it from a garden center. Make sure the bagged compost is high quality compost. Take a bag home and inspect it. It should be loose, light and not stink. It should be made from recycled yard waste, animal manures, or processed sewage. Many municipalities offer free or reduced cost compost made from yard waste.
• Peat - has excellent moisture-holding properties and is slightly acidic.
• Coir - is a good substitute for peat. It is madGarden Soil mixe from coconut hulls and is arguably a renewable resource, whereas peat is not being sustainably harvested.
• manure - most manures will need to be composted some before added to a soil mix. This is because they are high in nitrogen and need to break down some first. Otherwise the manure can burn plants, just like adding too much chemical fertilizer.
• mulch - mulch has some moisture holding properties, helps keep soil loose, and will break down over time. Mulch is a nice soil additive because local varieties are usually inexpensive. Mulches can be wood or bark mulches, and the finer ones work well in a soil mix. Don't forget to add some over the top of the soil after planting.

The above ingredients can be mixed and matched, along with yard soil if desired, to create a nice soil mix for raised beds. Keep the organic matter (manure and/or compost) high, and plants will be vigorous and healthy.