I'm looking at getting another Lens?

I have the nikon d90 and i'm currently looking at getting a more professional lens! I don't really know what sort i want. If you could let me know your recommendations, and some info about them, that would be great!
I'm studying photography

What kind of photography do you do, what do you find lacking about your current lens, and what lenses do you currently have?

If you can't name something that you find wrong about your current lens, then you don't need another - save your money then. Just randomly buying lenses without specifically knowing why one needs that particular lens is a great way of wasting lots of money.

Based on your description, i can't recommend getting a new lens. By the time you out grow your old lens, you ought to have a clear picture what you want to achieve.

Smaller depth of field, 50mm f1.8
longer zoom 70-200m f2.8
wide angle 14mm
macro 100mm f2.8

there are tons of other options out there. Until you know what you intend to use the lens for, you don't need a new lens.

My advise is simple. Wait until you know what you want before you buy a new lens.

Do you want shallower DoF or better low light shutter speeds? You will want something with a wider aperture.

Do you find you like more compressed compostions or like shooting from further away? Maybe a longer focal length is needed.

Do you like crazy stretched out compositions or massive feelings of depth or even like to get right up close and personal to your subject? Then maybe you want an ultra wide.

Is your ultimate goal to get the best Image quality (sharpness, colour rendition, contrast etc)? Then maybe a high quality prime.

There are many reasons to want a new lens and just wanting something a bit more pro isn't the best reason to get one.

Use what you have until you can't do something with it. When that happens you can look into the best lens to suit your needs.

Decide what your photographic needs are and what you are lacking in your current lens. This will then dictate your choice of next lens.

You say you want 'more professional', but the kit lens is capable of good shots in most conditions.