for concerts : nikon 85 or 105 in the aperture that you can afford, they will allow you to shoot without flash, I would suggest the 85 1.4, or the 1.8 if that is too expensive, get the af-s, 105 will give you some more reach.
for parties, you already have a 50mm 1.8, so add the 35mm to that and you are covered. small, light, fast normal lens, get the af-s
as suggested by drobs
travelling : 12 - 24 you already have for landscapes, 35mm, 50mm and 85 mm will cover the rest, should you require another lens will depend on you interest.
add the 70-200, big and heavy, but thats the price you pay for a fast lens and a tc1.4 or 1.7, if that is too expensive, then look at the 70-300 vr and you should be happy for a long time, unless you develop an interest in marco photography, but thats another topic.