Those are relativly easy fish to breed, however if your looking for something that looks a bit better (IMO) try breeding convict cichlids, they're just as easy to breed however they are VERY protective of the eggs and the young.
Guppies, mollies, swordtails would be great to breed. However be sure you have extra space as they multiply quite quickly and can be quite hardy. So be sure you have place to put the fry and that.
Yer not relating to the over-breeding bit.
Female guppies CAN give birth to between 20 and 100 young every 3 - 4 weeks (although most of the fry will get eaten unless you have dense surface plant cover, with frondy plants around the tank). Dunno much about mollies/swordtails tho.