General Synonyms:
* Veranda
* Gallery
* Stoop (a small porch at the entrance of a house)
* Covered walkway
* Patio (though a patio is usually unroofed)
* Deck (though a deck is usually raised)
More Specific Synonyms:
* Piazza (a porch in a warm climate, often with columns)
* Balcony (a porch that projects from a higher floor)
* Gallery (a porch that runs along the side of a building)
* Loggia (a covered porch with open sides)
The best synonym to use will depend on the context and the specific characteristics of the porch you're referring to.