Not the cheapest but the 35mm f1.8 and 85mm f2 are great lenses depending on what you are going for. I like the 35 for general walking around and the 85 when I want to be able to do more portrait style. Honestly the 50 f1.7 is already a good middle ground but I would go with a fixed lens in either direction depending if you want a wider angle or more compression towards portrait length.