There's nothing low maintenance in reef keeping. If you don't have thousands of dollars to spend on this over the course of the first year, you're just fooling around, and will quit / kill all of your animals. This applies, even if you have nothing but a hand full of 3 dollar damsel fish. That said.
I have a Hector's Goby, who is lovely, but just grazes the algae in the tank.
Clown Gobies are small and pretty and eat a basic diet. Many of them die for mysterious reasons, though.
Blennies are fun, but can bully some other fish.
Cardinal fish are a cheap, ecologically sound and easy to care for fish.
DO NOT GET ANY MANDARIN OR SKOOTER BLENNY! No matter what the dealer tells you, these are advanced fish for people with lots of experience and resources.