At the beginning of season 6 Ted attend's a wedding wher he mets The Mother. It isn't until the end of the season do we that is in fact Barney's wedding, now the question begs Who is the bride? I believe it is Nora, syre at the end of season 6 Robin had a look on her face of regret for tell Barney to go talk to Nora. But come on Robin being the Wife would be such an obvious thing for the writer's to do. So I believe that its Nora because Barney really felt something for her I mean his heart literally skipped a beat when he saw her at dinner.