Links:
I have placed a link to show other calculators that students can buy for my class.
I don't recommend the TI-30Xa.
It does not allow numerators on fractions to be larger than 100, which is a problem in seventh grade. It will do most of the work, but the kids don't like it.
I only placed TI calculators on my list because they are the ones I am most familiar with. Other brands also seem to be less user friendly so I don't recommend them.