What are some good lenses?

I have a Nikon d3100 with 18-55mm lens.
i have heard tamron lenses create good pictures. Which would be best but not too expensive (under $800). I mostly photograph people/portraits and animals. I know its not what lens but the photographer that makes better images but i woul like some different lenses to play around with.

For portraits, a 50 1.4 AF-S would be a great investment.