The group I have this year are a challenge. Most of them don't know their letter names, much less letter sounds, so I have to find ways to keep the letter front and center until they learn it. Constant repetition is the key, and so we do the Jump Shout!
I put duct tape on the floor in the shape of the letter. (This one is an F.) The letter is DIRECTLY INSIDE THE DOOR. To enter the room, they have to jump onto the letter and shout its name (or sound, depending on which one I tell them to say.) They love it! In fact, some sneak back into the line to do it again.
Considering we leave and re-enter the room an average of SIX times a day, that's a lot of repetition!