Just down Rte 89 about halfway to Ithaca is the Glenwood Pines Restaurant ("the Pines"), with good fish fry and burgers. There can be a wait on Friday evenings.
Adjacent to the south edge of Taughannock Park is Taughannock Farms Inn, an elegant restaurant with American style cuisine and great views. (Reservations)
On Main Street in Trumansburg is the upscale Hazelnut Kitchen (Reservations) For the classic small-town diner experience try out the Falls Restaurant, also on Main St. at the south end of town.
In Ithaca itself we like Taste of Thai Express on Rt. 13 and Maxie's (Cajun) on W. State St., Hai Hong (Chinese) on Dryden Rd in Collegetown and then Madeline's (Fusion), Cent Dix (French) and Viva Taqueria (Mexican), the last three all near the intersection of State and Aurora Streets near the East end of the Ithaca Commons. Actually, that section of Aurora St has many good restaurants; there's enough competition there that all of them compete to be great. Plum Tree, on Dryden Road in the Collegetown part of Ithaca, also has good Japanese food. For upscale Italian, try ZaZa's on Rt. 13. Finally, there is the Moosewood Restaurant, home of one of the first cookbooks to popularize vegetarian cuisine.
For good ice cream, try the Cayuga Lake Creamery, north on Rt. 89, or Purity Ice Cream on Rt. 13 in Ithaca.