I dont know about "good deals" but Walden-Galleria is the big mall in Buffalo. It has most major stores. There's a Burlington Coat Factory accross the street and a Target around the corner. It has a Cheesecake Factory & there are several chain restaurants in the area.
In Niagara Falls, New York there is the outlet mall right off the 190 (Fashion Outlets of Niagara). That has a new Walmart behind it, too. I find better deals at the outlets. Depends what you're looking for, I guess.
McKinnley mall is also pretty good, but Walden has most of the same stores and Mckinnley is a bit more out of the way. Sadly all of the Disney Stores in Buffalo have closed down. Add to that Scarborough and Yorkdale. I had to drive over an hour to get to one this past weekend. scary.
Boulevard Mall is close to the Marriott in Amherst. We stayed there last year before flying to Orlando and shopped at Boulevard Mall. I prefer it to Walden Gallery because it has all the stores my kids and I loving shopping at and because it's a smaller mall it's a lot less walking.
We are going to the Fashion Outlet Mall the day before we leave, plus a Target to get some snacks (and I love buying body wash there) to take with us to Florida. I put off my daughters back to school clothes shopping until out trip so that I can do it in Buffalo.
I second the Boulevard mall on Transit Road - close to the airport and all the same stores we love that the Galleria mall has. There is also a Walmart Super center down the road from it, and a Target.
And I 'third' the Boulevard Mall. We've stayed often at the Marriott, and the Boulevard Mall is nearby, has all the stores you need, and as PP said it's smaller (less walking) and is close to Target plus food stores if you need them.