Hawaii rentals such as condos, vacation rentals, bed and breakfasts, cottages, and cabins are the best way to save money in Hawaii, and they normally give you more privacy then hotels, sometimes with full kitchens and other amenities.
Poipu Area
Poipu is on the South Shore, home of the famous Poipu Resort and Poipu beach. Koloa, Kalaheo, and Lawai are also in this area.
Princeville Area
Princeville is a grand resort area on the North Shore near Hanalei Bay.
Waimea Area
Waimea is on the South Shore, at the entrance to the Waimea Canyon. Kekaha and Hanapepe are also in this area.
Lihue Area
Lihue is where the airport is, on the Southeast shoreline. It is the largest city in Kauai (but still not too big), and home to Nawiliwili Bay.
Kapaa Area
Kapaa is a central point on the East Coast for exploring both the South and North Shore. Wailua and Anahola are also in this area.
North Shore
Here you will find rentals outside of the Princeville resort, but still on the North Shore; areas are Kilauea, Hanalei, Haena, Anini Beach, and Kalihiwai.
Multiple Vacation Rental and Lodging Websites
If you can't find it on my site, here's a list of other Kauai lodging sites - you are practically guaranteed to find your perfect Kauai vacation rental or condo.