There's a couple things about Nikon lenses that you need to know, particularly if you're thinking of buying one of the modern Nikon camera bodies.

The current version of the Nikon lens has a designation of AF-S, which refers to the focus mechanism of the lens.  There's a secondary designation, "G" which is the lens series.  G lenses do not have an aperture ring on the lens.  We'll leave that to another discussion though.  You don't need the aperature ring on a modern camera anyway.

The simple explanation is that an AF-S lens has the focus motor in the lens itself.  This motor is what moves the all the bits and pieces inside the lens to bring it to a sharp focus when you press the shutter button on the camera.

Any other lens designation, and there are a ton of them, use a focus motor that resides inside the camera.  

Here's the reason why it's important - many of the modern Nikon camera bodies do not have a focus motor in them and therefore REQUIRE the use of an AF-S lens to work at all.  

Nikon is not great about explaining that and I almost fell victim to it just recently when I was looking to buy a back up body on the cheap and was about to pull the trigger until I decided to take another closer look at the camera specs.  Whew.

Now the reason why it's good to have a camera with a built-in focus motor is that it allows you to use older lenses, auto focus and manual focus.  The best of the older lenses are the ones that have a "D" designation.  These are great lenses, typically smaller and lighter than their AF-S versions and normally at least as sharp and absolutely more durable.  The one downside is that D series lenses tend to focus slower than the AF-S lenses and can have a  bit more trouble in low light conditions.

There is a subset in the D line and those have a designation of "ED" which indicates optically superior glass.  D series lenses are largely out of production but are easy to find used and are almost always a tremendous bargain.

I shop KEH.com for used lenses and they are the only place I trust.  I've never been disappointed by a lens I got from KEH.

If you're doing landscape or general use photography and your camera can use the D series lenses, I strongly recommend looking closely at the D series lenses before shelling out huge cash for the modern AF-S and especially the newest AF-S VR or VRII lenses.  

One caveat to that is that if you have a camera that's above 16 megapixels, and particularly if you get to the 24 megapixel range and above, then the most modern lenses will perform better with those cameras.  High megapixel sensors are not forgiving of lesser lenses and it does show up.  It's not a night and day difference though - you'll have to look very carefully to see any difference between a top end AF-S VR lens and an equivilent D series lens.  

For example I have a 80-200 f2.8 D series lens that is great and I like it a lot.  I also have a 70-200 f2.8 VR II lens that is even better in that it's sharper and I can really see a difference in my 24 megapixel camera, but do not see much difference in my 16 megapixel camera.  But the newer lens is bigger and heavier and cost $1000 more.  Is it worth that extra $1000?  No, not really.  And sometimes I regret that expense.

Also keep in mind that Nikon, like most any company, produces two or more lines of lenses for different target audiences and just because a lens has the AF-S or AF-S VR designation doesn't necessarily mean it's a good lens.  Read reviews thoroughly, lots of people have been down this road before and so there's plenty of opportunity to learn from others' mistakes and good fortune.