BA Executive Club has one-way awards too -- on itself and most other partner airlines -- at half the price of the roundtrip award level.
CX Asia Miles has one-way award options but they are generally lower than the roundtrip mile distance but more than 50% of the roundtrip cost.
BD Diamond Club has one-way award options at half the cost of the roundtrip award.
Those are the programs that I know to have one-way awards that are at a significant discount from the roundtrip award price in miles.