I am looking to purchase a navigation system for my car. I only want to spend (at the most) $500. -What is a good brand? -What kind do you have and do you like it? -What are some nice features to look for when buying a navigation system? -How exactly does loading the maps onto the system work? I noticed that a lot of them take SD memory cards. So do I download the maps and info to the SD card and then plug that into the system? This will be my first navigation device, but I consider myself to be pretty computer and technical literate. What brands do you think are better and why? -Garmin -Viamichelin -Nextar -Magellan -Whistler -Lowrance -Tomtom -Pioneer -Cobra -Uniden Thank you so much for your assistance!