Italianate and French - formal and/or bilateral symmetry
Tudor, Cottage or Bungalow - some symmetry, but less formal
Modern - crisp, clean geometric shapes and/or lines
These are merely historical suggestions from which you may start...there are endless hybrids and adaptations.
Remember that a truly successful garden design is not only aesthetically pleasing but also satisfies the needs of those using it.
from the office of Torrey Pines Landscape Co., Inc.