What's a next step up lens I can throw on my Nikon D40?

I'm thinking i'll use this one for travel purpose's, I was already looking at the NIKON 50MM/1.4 AF D.
Would any of you recommend it?

Added (1). I currently carry an 55 - 200mm and a 18 - 55mm with a D40

The 50mm f/1.4 is an excellent lens, but the 50mm focal length isn't very versatile on a D40. Try setting your 18-55mm to 50mm and you'll see that it's quite "zoomed in" all the time. I don't think it would be useful for travel.

For travel I would say the 18-55mm is the ideal lens, great for mixed subjects, landscapes, architecture, people. It's also light, and that's got to count for something.

If you really want to buy a new lens for travel, I'd suggest looking at the 18-135mm or 18-200mm so you can avoid carrying two lenses.

50 are not good travel lenses. The 50 AF will not autofocus with your camera, but the AF-S version will. The 18-55 you already have is a great travel lens. The 18-200 VR is a great travel lens too, the 50 isn't.

Those two you have will cover just about anything. The 50mm is more of an indoor portrait lens.