Camera lens suggestion?

I own a Nikon D80 and am planning to invest in another lens sometime soon.

Right now, I have an 18-135mm, a 50mm, and a 28-300mm. Any suggestions as to what I should consider next? Thanks!

Added (1). The lenses I have right now do overlap. The 50mm was a gift. The 28-300mm was inherited. The 18-135mm came with my camera. I'm looking for one that will do something that mine can't.

Eww you should of got a canon t2i…

These lenses already have a lot of overlap. I'd suggest determining what you need a new lens to do that your current ones can't. Just buying one to have another one makes no sense.

For example, if you need to use a 50mm focal length for a shot, which one do you use?

You have all you need to take good photos in many situations. I would wonder what kind of photographs you often get and would get a pime lens for that. Perhaps you can change any of what you own

So what are your lenses not doing for you? You have the full range from 18 to 300mm.
I see that all of the lenses you have are relatively inexpensive and not professional lenses. I'd probably start to replace those with professional grade lenses of f/2.8 or better.
First to go for me would be that 28-300 as it is pretty weak on image quality. I'd replace it with a 70-200 f/2.8. Depending on your budget they range from the tamron at about $799 to the Nikon at $2400.
That would allow you much sharper images, low light ability and a fixed f/. The image quality alone would be worth the investment.
If you aren't wanting to replace that one first, then the 18-135 would go and I'd replace it with something in the 24-70 f/2.8 range. Nikon's runs about $1600. Tamron produces a 28-75 f/2.8 that runs about $450 and is an excellent lens. Again, image quality would be GREATLY improved and low light ability, fixed f/.

The only other thing I could possibly think of would be the 35mm f/1.8 for Nikon. It's a much loved lens on the crop sensor bodies for portraits. The same low light ability as your 50mm and beautiful image quality.

Since you have 18-300 covered, I think you should invest in a wide angle lens. Something in the 10-22mm range.

The 18-135 is considered normal to slightly wide on the D80.