I lived there for a couple of years and it is a great town. Though I am not an expert on touristy things (WORK!!), my favorite part about San Diego and the thing that left a strong impression is the drive on the 101. Especially heading north from Torrey pines toward Del mar. The views of the beach as you clear Torrey pine, going downhill toward Delmar are beautiful... afterwards you could stop for a nice lunch overlooking the beach or simply spend some time on the beach!