You might find "Image: Designing Effective Pictures" by Michael Freeman useful. I got it on recomendation by somebody a while back, and am just starting it now. It's from the Amphoto workshop series, and has a number of projects throughout it. I just finished "Learning To See Creatively" by Bryan Peterson. Also basic, but helps to stimulate thought on composition- some good ideas. As others have said (as do these books), painters are good people to look to.