Here is a list of some of my favorite things on Kauai:

Breakfast:

NoKa Grill (Yum!) -- I share the parking lot with them!

Lilikoi's (Lihue)

Olympic Cafe (Kapa`a)

Tip Top Cafe (Lihue)

Daddy O's (Lihue)

Keoki's Paradise (Poipu, I think breakfast is weekends only)

Kalaheo Cafe (Kalaheo) 

Lunch or Dinner

NoKa Grill (Lihue, share the parking lot with them- breakfast and lunch only)

Rob's Good Times Grill (Lihue)

Duke's (Lihue, right behind my shop)

HukiLau Lanai (Near Coconut Marketplace, our favorite!)

Bubba Burgers (Poipu and Kapa`a)

Savage Shrimp (Poipu)

Keoki's Paradise (Poipu)

Olympic Cafe (Kapa`a)

Chicken in a Barrel (Waimea, Kapa'a, Hanalei)

Brenneke's (Poipu)

Golf

Hokuala

Puakea

Poipu Bay

Wailua (County Course -ranked #30 best in nation Municipal by USGA)

Kiahuna

Makai 

Kukuiolono

Boating / Sailing Trips

Holo Holo Charters 

Blue Dolphin

Kauai Sea Tours

Capt. Andy's

Makana Charters

Beaches:

Kalapaki

Po`ipu

Salt Pond

Brenneke's (for boogie boarding)

Hanalei (Fantastic sunsets in Summer)

Lumahai (for relaxing in the summer, not recommended in winter)

Polihale (better have a 4WD to get there)

Ke`e (Permit Required)

Kealia

Anini

Snorkeling locations:

Lawai Beach - For the experienced snorkeler (Spring, Fall and Winter)

Ke`e Beach (Permit Required)

Poi`pu Beach

Lydgate Beach Park (fantasic for families or beginners)

Tunnels Beach - For the experienced snorkeler -Spring, Summer, and Fall)

Lehua Rock (Available through Holo Holo Charters and Blue Dolphin)

Salt Pond Beach Park

Anini Beach (Honu, or Sea Turtles)