Ko Olina Lagoons
This was our absolute favorite beach, and we didn’t even mind traveling over a half an hour to get there, so worth it (Ko Olina exit off of Farrington Highway). The weather leeward was usually better than all other places on the island, so that was another driving force to get us there. Oh yeah and there was Tanioka’s on the way, the most delicious food we ate on Oahu and we brought it to picnic at the lagoons. All beaches in Hawaii are public access, so it is fine to go into the Ko Olina resort and beach it up. Wave to the guards and follow the main road in the resort, watch the signs and turn off at one of the lagoons. It has four lagoons that are relatively quiet and great for calm swimming. The lagoons are open ocean but have rocks piled up to block the huge waves from coming through and it filters back out. The water is gorgeous turquoise and the sand is perfectly yellow. 
You can also sit on the grassy area if you prefer that. If you come early enough in the morning, especially on a weekday, you may have a whole lagoon to yourself like we did. We went to three of the four lagoons. The first day we went to 4 because I heard it was the best. I would say it has the biggest sandy area and the biggest parking lot (so it’s your best chance on a weekend). Another day we came later and 4 was full, so we drove into check out 3 and it was full, and got lucky at the small parking lot of 2. Lagoon 2 had a different feel there were thatched umbrellas you could post up by for some shade, which was nice. Lagoon 3 also has a small lot but we checked it out one day, it’s not too different from the others but it’s right by a snack bar. All of the lagoons have restroom facilities and showers. There are fish in the water (they swim right up to you if you stand still, and many people snorkel here in the calm waters). There are some birds with great little personalities, we found a little crab one day, and for some reason I had a few ladybugs landed on me another day. 
Lucky I guess! This is also a beautiful place to watch a sunset. 
As it is snowing here in NY today I really miss this truly amazing beach.
Electric Beach aka Kahe Point
This is a really quiet beach across the street from a power plant (92-301 Farrington Highway, Kapolei, HI 96707). 
It supposedly makes the water warmer which attracts fish (and therefore great for snorkeling), but we didn’t go in to find out. It’s also a bit rocky here, but great sand. The beach is beautiful and peaceful, great for walking or sunbathing. We found a sea urchin on our stroll. 
This is a perfect sunset spot, nothing between you and the horizon.
Pokai Bay Beach
We only stopped here for a few minutes to check out a three terraced heiu. 
We stopped on the way back from visiting Ka’ena Point and the beach wasn’t on the main road when reached the town of Waianae, so we headed towards the ocean and found it (85-037 Waianae Valley Rd Waianae, HI 96792 ). It’s a beautiful spot for a heiu, great mountain views, and supposedly a calm place for swimming. 
It has a parking lot and was filled with locals so it must be a good spot. We spotted this pretty yellow bird when walking back to the car. 
Would have loved to give this beach some more time!
Ewa Beach
This is one beach I didn’t research at all, on our last night we just stumbled upon it and waited for a sunset. 
We took Ewa Beach Road (in the town of Ewa Beach) all the way down and then followed our senses through a residential neighborhood until we found a beach access sign. We parked, smiled at the friendly man who lived there, and walked on in. We spread out a towel and read until the sunset, trying to live in the moment and not think about heading back home to NY. This was a really quiet seeming beach with a view of Waikiki and close enough to the airport to see all of the planes coming and going. 
I’m not sure about the water but the waves were steady and the sand was comfortable. The area of beach is a bit small, and there is a drop slightly steep off when you get closer to the water. It fit the bill perfectly for us, we were lucky to have found it.