You don't have to jet off to an island to find gorgeous beaches and all-inclusive resorts. Costa Rica has plenty, and it's right here on the continent. From the incredible biodiversity of its forests to the numerous volcanoes to the picturesque beach towns, Costa Rica has an array of things to see—and you can either use the resort as a launch pad to go explore, or you can take it as easy as you dare, never setting foot in a place where your drinks aren't free. It's up to you.
Hotel RIU Palace Costa Rica
RIU actually has two resorts right next to each other in Guanacaste, Costa Rica. Of the two, the Palace seems to me the most well-established, and—for now—the most well-regarded of the two. The hotel offers one buffet and four themed restaurants, an ice cream parlor, and something like six bars, a couple of which never close, in case you want to get up and walk around. If you don't feel like going out, there's also 24-hour room service and free Wi-Fi. There's a spa, steam bath, fitness classes, and whirlpool, as well as a casino. And the staff are happy to arrange excursions to nearby golf courses, though that's not included in the hotel stay.
Doubletree Resort by Hilton, Central Pacific
You don't often find a Doubletree that's all-inclusive, and you don't often find an all-inclusive that puts a cookie on your pillow, but here's the best of both worlds. In part possibly due to its incredible affordability, this Central Pacific resort is, among other things, a favorite among locals for staycations. There are four restaurants and seven bars, including a "fruit bar" with fresh fruits and shakes, a swim-up bar, and the "Sunset Bar," which opens on weekends on a private dock just so people can appreciate the sunset. Entertainment ranges from water polo and kayaking to foam parties and dances with live bands. Wi-Fi is not free in the rooms, but given the price versus other all-inclusive resorts, you can probably afford to pay for it. You'll also find a spa, tennis courts, and a teen's club.
Flamingo Beach Resort and Spa
Flamingo's All-Inclusive plan is one of several packages offered by the hotel, and as such, it's a little more restrictive than some of the others. You get three meals a day and unlimited house beverages (limited to two at a time), along with unlimited use of the tennis court and fitness center. But it's not a "24-hour room service, clean out the minibar for free" sort of deal. That said, the staff is routinely singled out for praise, and families in particular rate the hotel highly.
Allegro Papagayo seems to be a good middle ground for affordability and exclusivity based on other Costa Rican resorts. Your package includes food and drink at the three restaurants, snack bar, and three bars. There's a large pool, a private beach club, and a kids' club that provides supervised activities while parents enjoy themselves. They also provide land and water sports, from darts to volleyball to water polo. Kayaking, snorkeling, scuba, golf, and transportation are not included, but honestly, that seems to be part of the scene here in Costa Rica. "All-Inclusive" takes care of food and entertainment, but the "extras" are very often extra. Visitors also note that friendly monkeys roam the beach and are part of the draw for some people.