If you don't mind the babies being eaten (and the adult guppies would do that anyway) how about golden barbs, rosie barbs, bristlenoses, corydora catfish, loaches (but watch out for clown loaches because I believe they uproot plants).
I have those fish plus a female siamese fighter, some currently small angels, golden and blue gouramis, and a couple of bolivian rams.
Platys might be good too and would add colour
Cheers
Jude