Guppies are known as livebearers and are an ideal community tank fish,so to answer your question, any community tank fish would be compatible.
Now you are probably going to ask what others are compatible. There are several species, depending on your taste. I hate TELLING people what they should have in THEIR tanks, because it is a personal choice.
Fish such as Platys, Swordtails, Neons/Cardinals, depending the size of your tank, you could have some Mollies.
The best advice that I will give you if you have no idea at all how you would like to setup is, have some fish for all levels. This way it is pleasing to the eye. With my first tank some 26 years ago now, I started off with guppies and swordtails for the top, neons and cardinals and harliquins for the middle and bristlenose plecs and corys for the bottom. My tank was 24X12X15. I had about 23 fish in all, probably a little overstocked but I had a good twin UG filter system and plenty of airation powered by the old Whisper twin airpump. I also added a small power head on the surface just to give a bit of "current" effect to the water.
