Well in short the answer is all of them but here are a few that are PARTICULARLY low skill high reward for new players learning protoss.
5)pvx photon cannon rush. This is a classic and talking about it would be like beating a dead horse.
4)pvt dark templar. you can make a normal base if you want but it doesnt actually matter how well you macro. just send the dts in and cross your fingers he doesnt have a scan you will straight up win 9/10.
3)pvz proxy 4 gate zealot. want to know how to beat any zerg player bellow master 3 100% of the time? build 1 pylon. build 4 gateways. none stop zealot production. THAT is the build and it works every time. if you are bellow 4.3k with protoss you should try it against zerg i guarantee you will win every time with it.
2)pvt, proxy void ray. no explanation needed really.
1)pvt charge all in. There is not a build in the game that is closer to cheating than the charge all in. There is almost no way to hold it and prince managed to beat maru with it even though maru is 10x better. If you have ever played vs this build. you would know how op it is.
so blizzard if you are reading this plz nerf.