HST, German volume training, Dual-Factor Hypertrophy training, HIT, weiderism/old school, Reg Park/Steve Reeves training, Hardgainer (Stuart McRoberts) training . . .
That's what comes to mind initially. A google search on any one of these methods would get you started. From the above list, I would recommend the dual factor (5x5, DFHT, or GVT) methods or HST.