お疲れ様です(Otsukaresamadesu): Which is basically like thank you for your hard work. You say it when you end pretty much anything. It could be an interview, a day at work, a phone call. My navigation system tells it to me when ever I'm at my destination. Lol
一番の宝物 (ichiban no takaramono): It is the name of a Girls Dead Monster song, but saying it has so much emotion. I tell it to my dog saying 「あんたが僕の一番の宝物」 which says that she is my best treasure.
これはペンです(Kore wa pen desu): It literally means "This is a pen." I was watching AbroadInJapan on YouTube and he said that this is a term to break the tension in a heavy atmosphere. It's a very simple saying. So saying something so plane and redundant is always funny, so I say it all the time just to have fun.