Thanks for all the replies everyone

... I've narrowed my decision down to a purchasing a Nikon but for the sake of time will I be able to produce "professional quality" images with a $500 dollar or less camera?
First off "professional quality" is a misnomer, as applied to equipment. In the hands of an artist, a work of art can be produced with nothing more then a simple pin hole camera. As others have mentioned photography encompasses more then equipment. First and foremost are the elements of visual design. Photos need order, to guide the viewer things like Lines, Shapes, Form, Textures, Patterns, and Color emphasize order and create visual interest. Without these, images taken with the most expensive camera will only be snapshots. Take some time to study the basics of composition. An excellent read is "The Photographer's Eye", by John Szarkowski, if your local library doesn't have a copy you can find it here used
Amazon.com: Buying Choices: The Photographer's Eye or I stumbled across a new release (same material) in a Barnes & Noble at a much higher price last week.
I know you've indicated an interest in a wide range of subjects, but narrowing the field will help you choose equipment more wisely, to produce acceptable results. For example, shooting nature or sports, you'll likely want a lens with a longer focal length, as opposed to landscape where a shorter focal length is required. Camera equipment is a tool, you wouldn't try to cut down a tree with a handsaw, nor would you want a chainsaw to cut a piece of wood trim. DSLR bodies can be changed out, lenses can be changed out, however there's not a lot of interchangeablilty between manufactures. Once you pick a brand you're locked in, so choose wisely. If you do, you'll have basic building blocks that you can build on as your experience level dictates.