Lens Help for Nikon D7000?

Currently own a Nikon D7000 and all Nikkor lenses although I'm willing to use sigma, tamron, etc. I need a good landscape lens. I bought a Nikon Normal AF Nikkor 50mm f/1.8D Autofocus Lens thinking it would be decent for both landscape and portrait but was easily disappointed when I found it failed tremendously doing landscapes. Although the lens is beautiful for portraits and is now my favorite portrait lens I own! I'm looking for a good landscape lens for sunsets and a trip to Europe. Budget is between 0-600 USD. I perused a little on my own and found a Sigma 10-20mm wide angle but did not know if that would be good for me. Also I would like the lens to be good at long exposures but also have a fast AF if possible.

50mm is short telephoto for your camera and yes, it is perfect for portraits. Normal for the D7000 is 35mm. Landscapes are best shot with wide angle - 12mm to 24mm. Lower than 12mm is fisheye and you wouldn't want that much distortion on landscapes.

http://keerok-photography.blogspot.com/2011/05/lenses-so-many-of-them-there-is-no-best.html

If you have the 18-55mm or 18-125mm kit lens, the 18mm end would be good enough for most landscapes.

I like using a 28mm wide angle Lens you don't get a fish eye affect, and it works real nice for pictures of large views or in your case landscapes.

First I would recommend going to a photo store and trying out a few lenses.
Only you can know what you really need.
I would recommend the Nikon 24-85mm lens.

http://www.amazon.com/...008B14TQ6/

It is right in your price range.
Some people complain that it fills like a kit lens, but it is actually a really good lens.
Here is a great review.

http://kenrockwell.com/...5mm-vr.htm

It is a great all around lens.
It is fairly wide too.
I would not get the Nikon 18-70 or 18-135 because they have no VR witch is a big draw back.
I would stay clear of the Nikon 18-105mm lens because it is very fuzzy at 18mm.
It also has a cheap plastic mount. Just asking to brake.
The 24-85mm lens really seams to be right for you.
It is an FX lens witch is really good.
Because it is FX lens you will be using the best part of a really good lens.
You are shooting with a DX body, so the sensor is smaller then a full frame camera.
You will be using only the best part of the lens because of the smaller sensor.
The center is always the best part of the lens and you camera will be shooting through that.
That will make your pictures even better, sharper and have less distortion.
If you want to get a prime lens get the Nikon 35mm f/1.8 lens.
It is a fairly wide lens. It also has a big aperture.
That will be great for shooting at night.
f/3.5-5.6 is just fine for long exposure though.
Just set the ISO at 400 or something and you are good.
I would stay away from Sigma ETC.
You will just run into compatibly problems ETC.
They are not built as well as Nikon too.

It all comes down to your personal opinion.