Just as you leave the Lihue area towards the South Shore, you will pass Kilohana, a sugar era plantation. They have Gaylords ,a fine restaurant, maybe not the best food on island, but the service is everything you expect at a table with white linen.
Poipu is one of the most popular resort beaches on the whole island, however, when the mom Monkseal returns each year to give birth, that area is cordoned off and kapu to the public so mom and pup can continue undisturbed. This is a great place to snorkel in the winter months. Consider having dinner at Brennecke's Beach Broiler across the road, and schedule it so that your dinner coincides with the sunset. Call for reservations, so you'll have a prime viewing table waiting for you; they can tell you what time is best for catching it. Their salad bar is superb. If you were to pass the turn for Poipu and continue on down the road, you could turn right into the Hyatt Regency and head down to see Shipwreck Beach. Walk down to the left end of the beach and lightly scramble up the cliff. (Kids do it barefoot; it's not a hard climb.) The ridge top you're now standing on is a wonderful hike. Follow it three miles down to the sacred land/beach called Maha'ulepu. They want to make a resort out of it, but have been thwarted by the discovery of a rare, blind, hunting wolfspider who lives in the caves there. It is the only place in the world where this species of spider has been found. There is a growing grassroots effort on island to prevent development from touching this pristine area, we say "Malama Maha'ulepu", respect Maha'ulepu. If you are a rider, this is where you should hire a horse tour. From the main road, take the right turn indicating the way to Spouting Horn, and follow the ever narrowing road around, past the little marina, up the hill, to the parking area on your right. During whales eason, December-March, this is an excellent whale watching spot. The"horn" of lava jutting out into the ocean is riddled with lava tubes and openings through which the sea bursts forth every few minutes or so. It is safer to view it from above, on the walkway, behind the fence. It is not forbidden to go down on the horn itself, but it isn't wise, either. By all means, avoid placing yourself between the ocean and a spouting area. This is a lovely place to watch the sunset. The marina you passed getting here has a perfect kayak launching spot; just park across the road. Spouting Horn's parking area is filled with little craft vendors under awnings; they have some very good bargains at this particular craft fair.
Our favorite South Shore hotel is the Hyatt. We go there for mini-vacations. The pool is INCREDIBLE and does not close. The Spa is considered one of the best on island. If you get any Spa treatment you are welcome to stay for the day. We love the Eucalyptus steam baths (yes, they are sex segregated, but there is a common area pool).Wednesdays they have a luau and the imu cooked pork is the best on island. All you can eat and drink, so get a room! I like all of the restaurants and the breakfast buffet, but Dondero's is the best Italian on island.
Some of the best restaurants on the island are on South shore, if you are going to bust a hundred on a dinner this is the place to do it. The two most well known are Roy's and Beach House, Roy's is in a bit of a slump, so the Beach House is king of the heap right now. When you call the Beach House they may tell you they do not have an opening for a week, so think about calling ahead. Or, the bar opens at 5:00 PM. At 5:30 you can order appetizers (PuPus) and at 6:00you can order off the menu. Get there at five minutes to 5:00 and you are in. A new restaurant, Red Salt is now open in the exclusive Koa Kea resort; it was enjoyable, but not in the highest tier (the Koa Kea is near the Marriott's Waiohai Beach Resort). Another great place is Merriman's Fish House, second only to the Beach House. Downstairs they have burgers and such, upstairs, fine dining. At any of the restaurants in the paragraph you can expect to drop some significant dinero. There is also a Mexican place, Tortilla Republic. I would avoid the lunch menu, but upstairs for supper is better. However, it is next to Merriman's and will cost 80% as much.
It wouldn't be right to mention South Shore and not mention Pukka Dog. We have never eaten their, but our friends are managers and apparently people love it.