I have the Tamron 17-50 and it is a SUPERB lens! It hardly ever leaves my camera to be honest. I love how much I can get into the shot (it shoots wide).
It is also very sharp (especially at f5, 5.6, 8) and fast. I totally recommend it!
Now there are a couple of other options...
New Nikon 35mm f1.8 - very good lens, fast and sharp. And it is shorter/wider than the 50mm. It is also reasonably priced.
As a contender to this one... a more expensive Sigma 30mm f1.4 - lovely lens.
But for your use, to cover the kit lens - I would recommend the Tamron 17-50.
I actually think it has a more practical range than the 28-75mm.