Both of these restaurants are in Ortigia:
Ristorante La Medusa specializes in seafood - and HUGE portions. My pennette alla Norma (with eggplant, tomatoes, ricotta, and basil) was amazing; it's what we think of in America as "red sauce Italian food," only 100 times better. But the portion was American size - the only time I've ever encountered that in Italy. Then, my friend and had each ordered the zuppa de pesce, picturing something like bouillabaisse. Instead, we got a huge plate of various kinds of seafood in the shells, as well as a whole fish AND slices of swordfish (a local Sicilian favorite). It was extremely heavy, and about twice as much as we could eat (although very tasty). Quite an experience.
Trattoria da Mariano: this was recommended by our host and was listed in one of our books. The food was OK and the price was low. But the service was abominable, as if it was their first day open. In addition, unlike almost all the other places we ate on the trip, there were no Italians eating there; the fellow at the next table who spoke fluent Italian turned out to be from Spain. One of the few places we absolutely wouldn't go back to.