I am just starting to do photography as a serious hobby, so I've decided to go ahead and purchase a Nikon D90 here in a month or so. I know most people have more than one lens. What lenses would you recommend and why? Also, what other accessories should I consider purchasing? My main focus is on shooting portraits/nature photos, if that makes much a difference. I have no experience with any camera besides 35 mm and my point and shoot camera, so if you could be specific I'd appreciate it.