I have done rides in the area while staying in Rehobeth but can't direct you to specific routes. Search in mapmyride. There are some nice rural road rides west of the beach. If you want a pleasant cruising ride head North along the beach road to Rehobeth and then either further north into parkland along the beach north of Henlopen Acres or along the bike path to Lewes. You can also just ride south along the beach toward Ocean City and back. Shoulders are pretty good.