Have you tried integrating what you are teaching with what the social studies teachers and/or the science teachers are teaching? If you do that there are lots and lots of fun activites you can do...
Also, keeping your students attention is not just about fun activities...though it helps a lot

. There are many "tricks" you can use to keep their attention. Simple strategies like the
pair/share,
checking-for-understanding,
all-write, etc. will keep your students much more attentive in class. I write about many of these strategies in my classroom management e-course here:
http://www.Classroom-Management-Tips.com Hope that helps,
Adam