I'm not in downtown very often for lunch but maybe try Sonoda's or Sushi Sasa. I haven't been to Sonoda's in awhile and Sasa is good but a little too trendy for my taste. It's not sushi but you could always check out Tag Raw Bar for something different but a "little" sushi related.
I also know that Blue Sushi & Sake Grill opened up recently. It's a chain and I can't attest to it but thought i'd at least provide the options I'd consider.