IN STORE ONLY. Not sure if this is a great deal, but it is much less that I've been able to find it.
ABC Warehouse (locations in MI, OH & IN) has the TC-P42X3 on sale for $388, IN-STORE ONLY. The sale runs through Saturday and they had several in stock at my local store.
WARNING: According to the salesperson at ABC Warehouse, they don't allow returns of plasma TV's except for a replacement if it is defective. Best Buy will price match, although my local store manager refused to do it and I had to call the customer service (1-888-bestbuy) to get the match. In his defense it was Monday and their policy states they don't match sales from Thursday through Monday of Thanksgiving weekend. In my defense the sale is good until this coming Saturday, so it wasn't just on sale Monday.
Since I can't post a link (must have 3 posts first) just go to abcwarehouse's website and search for TCP42X3.