Don't throw away your coffee grounds or egg shells, instead as you turn the potting soil in your house plants, add the grounds and shells for healthier house plants. This can also be used in vegetable gardens for larger crop yields.
In the continuing battle between gardeners and slugs, some people have tried coffee grounds to ward these voracious eaters away from their tender plants. This is a page about use coffee grounds to deter slugs.
This is a page about getting free coffee grounds for your garden at Starbucks. Starbucks and other coffee shops offer free grounds to their customers. These bags of coffee grounds are a good amendment for your garden soil.