Hadn't looked at this thread in a while...
For the Big Island... Hamburgers - can hardly go wrong at Splasher's across from the pier in town. This is one of our favorite all-around restaurants (good breakfasts, good burgers, interesting good dinner specials). Don's Tiki Bar has a couple of very good burgers, try their sweet potato fries with the burger, Don's tops my list of best places to have a maitai at sundown. Drysdale's big burger is good. Heard good things about Jackie Rey's burger but haven't tried it. A very good 5-6 buck burger - Pine Trees Cafe. Seeing as how this is a "divers" message board, Kalama's on the way to Kealakekua Bay has an OK, but kinda spendy, burger.
Best restaurants without blowing a huge hole in your wallet? Call Keei Cafe (cash only) in Kealakekua and Jackie Rey's the tops. At the resorts both would command a higer price. After that I'd say Don the Beachcombers, and then off all things, Splasher's. I've always liked the Kona Inn Restaurant, but haven't eaten there other than the oceanside bar area in years. Huggo's has a better lunch than dinner reputation among some locals... kinda busy at dinner, I tried it and everyone in my group had overcooked meals, I'd try lunch.
Interesting flavors? Check out Rapa Nui in the Banyon tree mall (or something like that), it's a small 6-8 business shopping court across from the main seawall in town under the banyon tree, behind the jewelry store. Kind of a pacific/indonesian fusion flavor place at a decent price.
Best breakfast? Check out U-top-It for crepe style items and a few other interesting items (I like their take on a spicy loco moco), Lava Java looks good... I've yet to eat there, too crowded for me. Splasher's has a surprisingly good breakfast, actually our favorite in town. My wife loves the crabcakes eggs benedict (yummy, I wanna say they're $13, eggs benedict on biscuit will cost you $11-$14 anywhere else in town if they have it), I usually pick one of their interesting breakfast specials. If you're staying up north, and diving out of Honokohau Harbor, stop in at Pine Trees Cafe for a quick breakfast on the way rather than spending 10-15 bucks for a ceral and a grapefruit at the Hilton... gotta admit, I haven't tried it, but I've heard good things (I like Pine Trees Cafe's offerings in general).
Best Mai-tais... Don's tiki bar (can't beat the view). Keei Cafe (interesting li heng mui spice involved). We liked Jackie Rey's mai-tai as well. All the others suck... just kidding... haven't had time to check out everyone's mai-tai.
Best Buffet? Gotta mention this. The Surf Sand And Stars Buffet at the Four Seasons on Saturday nights is kind of special. If you're OK with an 82 buck buffet, it's wonderful, especially if the weather is cooperating. Back in the day, before the big earthquake, the Mauna Kea Sunday buffet was special, about 42 bucks, haven't tried it since they've reopened - assuming it still exists.
Best Pizza? Kona Brew Pub is always recommended. Depending on tastes, check out Mahina Pizza Co. and Pizzeria Zacchini above Costco.
Best deal? 6 tacos for $3.57 at the newly opened Jack in the Box off their value menu (I ate there today, there's no accounting for tastes).