Here the Starbucks give away used coffee grounds for composting (works like a charm) but you have to get there first thing in the morning, because there's always some greenthumb old lady who tries to scarf them all at once.
At the end of the summer, after you've done your final weeding, get some bags of leaves (like the ones that fall off the trees in the fall) and spread those over your garden. As they decompose, they will organicise your soil and also act as a weed barrier, since the sun won't get to the soil during the winter.