I'm as skeptical of snake oil cans as the next guy, and I'm sure it's not as effective as an engine tear down and proper coating, but as a mid life freshen up, Liqui-Moly sell this:
LIQUI MOLY - Motor Oils, Additives, Car Care - Cera Tec - ceramic-based premium oil additive for extreme high loads
It's OEM approved and independently tested, and I've been curious to try it out for a while. I'm thinking of trying it on the Prius and Jeep (UFI already has coated cylinder bores).
An interesting test: