Tess, have you tried contacting your local landfill? Many County landfills now make excellent compost. Some sell it and load it for you, others let you have it for free if you bring your own containers and load it yourself. Compost is "garden gold". Nothing better you can put into your garden.
But if you can get composted manure, it is fine as long as it IS composted enough. It contains soluble nitrogen that can burn new plants, but if you work it in, water it for a few days and then plant your plants it should be fine.
Anything with a high proportion of organic material (anything that used to be a plant) is good. My favorite for amending planting holes now is alfalfa pellets. You can get it in 50lb bags from any feed store as horse food. I'll put anywhere from a cup or two in a smaller planting hole, say for a daylily or small perennial, to a pound or two for a small tree. Spread it around, dig it in, water and let it break down. The plants love it. I also amend with alfalfa pellets around my existing plantings in the early spring just to give the soil a boost. We have nothing but sand down here, and with our heavy summer rains and heat, the organic materials disappear pretty quickly.
