Hajimari no asa ni hikaare.
This is by far a very very big favorite for me, particularly because it is always used to wrap up some really awesome finishing scene or cliffhanger, and also because I've gotten addicted to it, I just open youtube for the sake of listening to this song. Or maybe its just because Hojo Kuniko is so awesome.
Honjitsu Mankai
Anything Hinagiku is highly popular in my books, and this just trumps all of them. A Hinagiku ED theme for Hayate no Gotoku has always been a wet dream of mine, and it has come true. One comes to wonder if it is possible to exert influence in an universe by simply wishing for something. Apparently it might just be possible.
Tomare!
Speaking of exerting influence with wishes, it should be no surprise the new Haruhi ED appears on this list. I'll let you guys who haven't read the novels in on one little secret: The ED spells out the entire second season coming. Which is awesome. It is basically the story in a nutshell sung out to you. Though, those of you with little imagination and no ability to grasp deep meanings will find it difficult or useless to try. It is better that you don't because it will completely spoil the rest of the (very exciting) story that is coming up.
Again
Another excellent OP for an excellent series. The songs chosen as the OP and ED themes for Full Metal Alchemist has never disappointed me. Again is a wonderful song to sing, and for some reason I just love it (maybe it tickles my music nerves in a certain way), and you'll see chords for this on the music page soon. (I've got a list of songs queued up for pages in the music page).