Got flat doors? Want a little enhancement? Check out Ron Hazelton’s tutorial on DIY door augmentation. It’s a relatively simple process that gives slab doors a recessed panel look. Note: Ron assumes some woodworking ability for the DIYer; however, it’s still a nice tutorial.
An alternative to Ron's molding idea is to apply (with finish nails) recessed door panels directly to the flat door for a dimensional look. Recessed panels are often sold at big box stores. I found the ones pictured below at Menards.