Most of my experience is with cichlids. Convict cichlids will breed even when you don't want them to and are excellent parents that will protect their babies against all threats. I've seen a convict pair keep two large Oscars isolated to one third of a large tank because there were baby convicts on the other side.
Brichardi are also excellent parents and will fill as much of a tank as you give them. They form colonies and juveniles will help rear the later batches of fry. It's pretty cool to see.
Neolamprologus Leleupi can also be pretty easy. Give them a cave, good food, and clean water (high PH and hard) , and they will breed.
Electric yellows, jewel cichlids, and Aulonocara are also easy to breed and are good parents.
Julidichromis Marlieri and Julidochromis Transcriptus will breed if given good conditions and lots of rock work. Juveniles and fry will hover around, hugging the rocks as they look for something to eat. They are very fun to watch.
Cyprichromis have interesting courtship that us easy to observe. They don't do much to protect their young after they are free swimming, but they won't eat them.
Synodontis Lucipinnus and S. Petricola are both easy to breed, but I had to use egg traps to preserve the eggs and fry. The parents will eat any eggs that they find.
I agree that bristlenose plecos are another fish that will breed if given half a chance. Some males will scatter the eggs instead of protecting them. Having an egg tumbler is helpful for such occasions.
I need a few more tanks so I can raise some of these cool fish again.