Unless you employ kindergarteners, grown people will not be excited by a scavenger hunt. And while i didn't really understand the Name Tag thing, that doesn't sound like it would boost morale either. And, of course, the crazy shirt day will not only not boost morale, but it will make people annoyed. At least that's been my experience with crazy shirt fridays at some companies. Although I would have to say it depends on the age of the employees. Older people for some reason seem to love crazy shirt fridays, while younger people (20's and 30's) are annoyed by it.
Something that I've seen done before that I found fun and so did the other people, was a bingo-type game. You make a 6x6 table for example, and you put different things in the boxes that people may do. IE: One box would say "born in another country", another would say "have been skydiving", another would be "can play the saxophone", etc. Then you print these out and give it to each employee. You give them 5 mins to go around and get other people to put their names down on the box that applies to them. When somebody has a full row, they yell bingo. Then you check their board and ask the other people to either demonstrate their talent (IE: if they put their name down on "can dance the Cotton Eyed Joe" or "can do a hand-stand") or to just confirm that they have done or know about what they put their name down on. This is a fun activity and again, gets the co-workers to get to know each other a little bit better. From my experiences, morale is greatly improved when the employees have a close-knit work environment and are friends with their co-workers, as opposed to when everybody is kind of isolated and just comes in to work, does their job, and goes home.
Another thing I just though of that may also help (depending on the age of the employees and their interests), may be organize a couple of sports leagues. If you throw in a PS2 or ping pong table in there, organize some tournaments for it. Maybe an ultimate frizbee league during lunch or after work. Something active and again, something that brings the employees together.
Finally, any kind of free food is a great idea! That will boost morale, give people some time to relax and talk with each other, and keep the employees fed.