I say livebearers, especially guppies. They're called million fish for a reason. =]
Most livebearers are already pregnant at the store so you can simply buy a female and chances are, she's pregnant. They can store sperm for up to 6 batches of fry so even without a male, she's still be able to give birth. Gestation period is on average 28 days but it could very well take up to 3 months for her to deliver depending on water temperature and conditions.
With cichlids (I've never bred them but this is what I've been told), not all are compatible with each other. One has to lay eggs while the other fertilizes them. Most are very protective of their eggs but by no means does this mean they will succeed at protecting them. If there are other fish in the tank, it's possible that the eggs will still get eaten.
