ideas for grade 4 math and technology

I'm a grade 4 teacher in BC, Canada, and I'm enrolled in a post-grad. program in integrating technology in teaching. I am looking for ideas to integrate technology into math lessons (starting with whole numbers to 10 000 and addition to 10 000,) in order to better engage students in the lessons and increase their understanding of these concepts. Any ideas for sites, free programs, or lessons themselves will be appreciated. Thank you!