Neil Patrick Harris is an American actor, singer, director and magician. Prominent roles of his career include the title role in Doogie Howser, M.D., Colonel Carl Jenkins in Starship Troopers, the womanizing Barney Stinson in How I Met Your Mother, a fictionalized version of himself in the Harold & Kumar series, and the title role in Joss Whedon's musical web series Dr. Horrible's Sing-Along Blog. He hosted the 63rd Tony Awards on June 7, 2009, and the 61st Primetime Emmy Awards...(Wikipedia)

Nathan Christopher Fillion is a Canadian actor, well-known for his role as Richard Castle on the ABC series Castle. He is also known for his portrayal of the lead role of Captain Malcolm Reynolds in the television series Firefly and its film continuation Serenity, and to a lesser extent for his regular role as Johnny Donnelly on the sitcom Two Guys and a Girl.(Wikipedia)

Kathryn Felicia Day is an American actress, comedienne, and writer. She played the character "Vi" on the TV series Buffy the Vampire Slayer and acted in movies such as Bring It On Again and June, as well as the Internet musical, Dr. Horrible's Sing-Along Blog and currently has a recurring role as Charlie on Supernatural. She is the star, writer, and producer of the original web series The Guild, a show loosely based on her life as a gamer...(Wikipedia)