It is difficult to find quality scans of video game art without doing some digging. The older a series gets, the harder it becomes. Luckily Kei, the creator of Dokuganryu (formally Be Your True Mind–a reference to the first Persona game), has amassed an enormous collection of video game art and scans from media that are difficult to find outside of Japan. The scanned media range from game guides to art and poster books.
The most exciting feature to me is a section devoted to MegaTen art. Some of these scans go back to the earliest games, and are of course in their original un-altered state, so they are high quality and generally very large files. As of March 15, the complete works of Kazuma Kaneko are also available. Any fan of the series should definitely check it out.