If you see the boiler (it is often on the wall in the kitchen) then try and check how high the heating is set and for how many hours in the day. If you are viewing in the winter this can give you a good idea as to how expensive the building is to heat months..
Keep an eye out for black patches and spots on the walls, bathrooms and kitchens can be particularly affected. Damp isn't very good for your health and will either mean that the building is poorly insulated or badly ventilated, either isn't ideal!
Be on the lookout for mouse traps, droppings and other signs of unwanted flatmates
Often important, everyone needs their privacy and security but many landlords will not put locks on bedroom doors (often because of issues with the television license!) A small lock that can only be operated from the inside of the room does not change the legal status of the house, so don't let them fob you off.
The easiest of the bunch to spot and probably the most important, student houses are a dream for any burglar so every extra deterrent is great, and of course it goes without saying that working fire alarms are a must have!
Check or ask whether the windows are double glazed throughout the house, this will make a big difference to your comfort and bills all year around so don't strike it off as unimportant. Modern windows will also have ventilation at the head.