#1 Seth Rollins - Wrestlemania 30
The most memorable cash-ins was also the best one as it had taken place in the biggest stage of them all, Wrestlemania. No one had ever cashed in at WrestleMania before, let alone in the main event of such an event. Seth Rollins' cash-in is probably the first thing that comes to mind about 2015's Wrestlemania; the second one, of course, being how Sting was screwed in his debut match in WWE.
Seth's run in the WWE championship match between Brock Lesnar and Roman Reigns to make it a triple threat contest elevated the already great main event and gave us one of the best Wrestlemania moments of all time. Despite being a heel, Rollins received a huge pop as the moment and the unexpected end to the evening was too good not to get a huge response from the crowd.
It also saved us from a calamitous Mania's closing moment as either of the winners wouldn't have satisfied the crowd. Lesnar was already hated as a champion due to his part-time status and nobody had wanted to see Roman in the title picture in the first place.