Basic compound movements to add thickness and density. Squats, deadlifts, weighted chins, heavy rows, etc., will all give you good musculature. It sounds as if you're diet is not "good" if you're training properly and eating enough. All too often you hear "I'm a hard-gainer" but in reality it's because most guys just aren't eating enough. Maybe list your training and diet here and some of us can help you out. I'm sure you're not eating enough though if you're training properly and not gaining.