What my next lens should be?

I just got Nikon d5100 and 18-55 lens, it is my first camera! So I have no knowledge in that field. What my next lenses should be? I only know I'm not interested in telephotos. Maybe micro, or just better lenses, some suggestion and information would be so appreciated.

Added (1). @Robert D

I was wondering the same is there a point to buy 50mm 1.8D lens when I got 18-55? Sorry if my question is lame, but as I said I'm new.

A wide aperture 50mm lens is a great one to start with. Shallow depth of field and high quality at a low price.

If a 50mm f1.8 interests you, get the 50mm f1.8G lens, not the D version which wouldn't allow autofocus on your D5100. Yes, it will benefit even though you have 18-55 lens already. Better control of Depth of field, less distortion, better low-light performance, better image quality all around.

For macro lenses, a 60mm f2.8 micro or a 105mm f2.8 would be right up your alley. If you want to save your pennies, a Sigma 70mm f2.8 EX or Tamron 90mm f2.8 are excellent budget lenses.

It totally depends on what you want to shoot. If you are keen on portraits/low light work then the 50mm f1.8 will be ideal. THe 50mm f1.8 will give you the same field of view as your kit lens set at 50mm, but the difference will be teh f1.8 aperture (as opposed to the f5.6 you'll get with the kit lens at 50mm) AND prime lenses are generally sharper than zooms.

The 50mm f1.8 comes in two versions - only the AF-S version will autofocus on your camera, the AF D version won't - you'd need to manually focus it.

As for macros, I'd recommend the Sigma 50mm f2.8 macro or the 105mm f2.8 macro - both are tack sharp. The 105mm might be better if you are getting a 50mm lens otherwise.

Aside from what's already been said, try going for vintage nikon lenses (AI lenses, because NonAI may not work on your camera.)
Get a vintage nikon 35mm lens (It will look like a 50mm on your camera) for $50 and it will feel nicer than any modern lens and will be just as sharp as the $200 50mm that's brand new!

Also you might want to stick to primes if you don't have much of a budget, because they will always have higher quality for price.