I'm looking for a new lens for my nikon d90?

Right now my considerations are the nikor 18-200, 55-300, 28-300, and the tamron 18-270. What are some off the advantages and disadvantages, and which lens would give better image quality? I currently have a 18-105.

Nikor gives better quality!

Experience makes it difficult to believe a third part lens, especially one from Tamron, will exceed the image quality offered by an OEM lens like those from Nikon. That's not saying there aren't rare exceptions from folks like Leica or Zeiss but, you normally pay a premium beyond the cost of an equivalent Nikon lens for such exceptions.

As for the lenses you're considering, most over lap the coverage your current lens offers by a wide margin. There's not a lot of point in owning both an 18-105mm lens and an 18-200mm or 18-270mm lens. Same for the 28-300mm to some extent but, this lens is also limiting you by taking away some of your wide-angle coverage. The only lens in the bunch that makes sense based on what you own is the 55-300mm zoom if and only if you need the additional telephoto covereage.

As much as I'd like to tell you to spend away and spend money on a new lens, I don't think your image quality will be improved at all if you buy any of the lenses you've mentioned. In fact, you're likely to get more significant improvement from spending that money on a tripod and a flash along with some classes on putting them to use. I'm saying this as someone who has spent well over $15, 000 on cameras and lenses in the last five years. The single biggest impact on the quality of my images in the last couple years hasn't come from bigger and better lenses. It has come from learning to use a flash. More specifically, learning to employ multiple flashes/strobes off camera in addition to expanding my knowledge of available light. You're mileage may vary but, I probably could have saved myself at least $10, 000 had I known then what I know now.

Before buying any lens, ask yourself a few questions.

"What will the lens do that my present lens can't do?"

"Why do I need a longer focal length lens? Do I really shoot sports or wildlife all that much?"

"Will a different lens enhance my photography?"

All of the lenses you list are lower-end variable aperture lenses and aren't going to help you in low-light situations. The 18-200mm lens would make sense if you sold your 18-105mm lens. A lot of people seem quite happy with a one lens kit using the 18-200mm.

In my opinion saving your money for the Nikon 70-200mm f2.8 lens would be your best bet to actually improve your photography.

I have the Nikon 18-200mm lens. Be aware that these lenses are technically "super zooms", and like all super zooms, it has a marginal image quality. I have found that when wide open, my 18-200 does have some soft areas. But when stopped down to f/8, it is as sharp as my other - more expensive lenses.

I bought the Nikon as it is not as extreme as lenses such as the Tamron 18-270, and I would suspect that a more powerful super zoom would have that much more of an optical issue.

Neewer 0.45x 52mm Wide Angle Lens does what it is supposed to - creat a wide angle @ 0.45x - it's a really low price but performs well. If you have a lens like 18mm with correct focus, it could creat a small vignette around the edges. What I liked was, that the lens had a macro in it too, so that's a really great addition!