What are some good lenses with big aperture for a D3100?

so a i just buy this camera (Nikon D3100) and these lenses SIGMA 18-200 f/1:3,5 - 1:6,3 , and i find myself complaining about the small max aperture of the camera, that really make it hard for shooting photos in low light , and don�t give such a high dof, and i was thinking about buying some lens with a bigger max aperture, it may be with a fixed focal length(i think a 18-55 would be more expensive, i don`t really know much about price tags) , but anything lower than 35mm, i tried searching for models, but i�m not sure when the models are compatible with my camera, i would really be thankful for any help