The last time I looked was over a year ago. I remember them having just one or two printers on the shelf that could do 11x17. Other stores such as Office Depot and Office Max had a much wider selection.
Here's what I'd recommend: Make note of the model numbers of any printers that you're interested in so you can look those up online. The computers in their store have Internet access, so use those to determine if it's a good deal (and take advantage of price matching).
Staples get's my vote on where to buy a printer. Best Buy has horrible service and a poor selection. As to the printer, I only recommend "Brother". The best printer ive had yet and ive had HP, Cannon, Dell, Lexmark. One of the best things about Brother is the fact that the ink lasts quite a while and you can print more for less.