Piers Anthony writes science fiction/fantasy all together. Some of his most popular series' are:
Xanth An open-ended series about a world where everything is magic or has magic. Each human has a magic talent that nobody else has. A king is the person who has the best talent. It is possible for women to assume the throne as King for the King is the human with the best talent, male or female.
Incarnations of Immortalitystories about the 7 incarnations of immortality:
Death (named Thanatos)
Time (Chronos)
Fate (Clotho, Lachesis, Atropos)
War (Mars)
Nature (Gaea)
Evil (Satan)
Good (God)
Mode about different realities all happening at the same time with a virtual mode that can cross them...
Aprentice Adept Two worlds:
Photon, a world run by science
Phaze, a world run by magic
I am a huge Piers Anthony fan as you can see. I am currently reading his biography "Bio of an Ogre" and have read all of the series' mentioned above exept Aprentice Adept which im reading the first book.