I came across these two websites recently while working on an interactive curriculum portal for our Language Arts Department. Both sites contain interactive activities and games for teaching Grammar.
Learn English was developed by the British Council. It is designed for ESL students, but the activities can be used in any elementary language arts classroom. There are a number of interactive activities that would present very well on a Smartboard. They can also be used in centers on classroom computers or on the Smartboard as well.
Road to Grammar Jr and Road to Grammar both contain a number of online quizzes, activities and games that can be used in an elementary classroom.
There are a number of websites on the web with interactive grammar games and activities. I found these two to be a couple of the better ones I reviewed. If there are others that you enjoy using with students please share them in the comments section.