Diabetes mellitus
Cranial diabetes insipidus
Cushing's syndrome
Renal:
Chronic renal failure
Relief of chronic urinary obstruction
Early chronic pyelonephritis
Nephrogenic diabetes insipidus
Fanconi syndrome
Iatrogenic:
Diuretic therapy
Alcohol
Other drugs, e.g. lithium, tetracyclines
Metabolic:
Hypercalcaemia (e.g. osteoporosis treatment, multiple bony metastases, hyperparathyroidism)
Potassium depletion (e.g. chronic diarrhoea, diuretics, primary hyperaldosteronism)
Psychological:
Psychogenic polydipsia (compulsive water-drinking)
Can't think of any more off hand...good luck!!!