How weird is it that the best Japanese food in the Loop can be found in Marshall Field's basement? At least they have the best maki rolls -- plump, fresh, tasty, and not very expensive.
Tokyo Lunch Boxes, on Wells between Washington and Madison, does a serviceable job, but in my opinion the rolls are not as good as Field's. TLB has a better selection, however, and offers hot items as well (which I haven't had) and will give you free miso soup if you order a gluttonous amount of food (which I do, regularly). It's a fine place, but just not as good, at least in the rolls department, as Field's.
Both places have regular sushi as well, and some salads, but the maki rolls seem to predominate the selection at both venues.