Pacific Coast Highway from Oceanside to the greater Torrey Pines area (where it is called Torrey Pines Rd.) is great. South of the UCSD campus, you can pick up the Rose Canyon bikeway from the south end of Gilman Dr. -- this will take you to Mission Bay, where there are ample places to ride. I also like the Fairbanks Ranch and Rancho Santa Fe area and the hills of La Costa and San Elijo. Several local shops will rent you a bike -- check with B&L Sports in Solana Beach, Nytro and the Bicycle Retailer in downtown Encinitas, the UCSD Bike Shop ("where cycling is academic"), University City Cyclery, and a couple of places in La Jolla or Pacific Beach.

Let me know as the date of your trip approaches, and we may be able to meet up for a ride. If you can ride a 57cm frame, you can probably borrow my son's 1980 Peugeot PKN-10, which he keeps in his apartment not far from your hotel. Another BF member borrowed the bike about 7 years ago and had a great time exploring San Diego County.