Teller West recently posted a video on YouTube showing how he performs OLL 20 using an algorithm from Wong Chong Wen. Antoine Cantin posted another way of doing the same moves. They use: R2 S’ R2′ U’ S2′ U’ R2 S’ R2′, but I find it easier to start with R2′, as it sets up your right index and middle fingers in a stronger position to do the S2′ double-flick. Note that at that point, your right thumb should only be on the upper front right piece, not blocking the S’ move. I use:
(R2′ S’ R2 U’) S2′ (U’ R2′ S’ R2)
I also show it can be employed to rotate two opposite centres 180 degrees on a supercube (one where centre piece orientation matters), using my Reuben King Cube. Put the opposite centres on the left and right, and do the algorithm twice. I used to do two T PLLs on each of those sides, so this reduces the move count from 14*2*2 (=56) to 18 moves. Much easier!
-Check out their channels for a ton of other useful tips.