I've seen some threads on message boards griping about the constant ads for some odd sale by Joseph A Bank, but respondents that have shopped there say their suits are actually pretty decent for the money; a step or two above what Men's Wearhouse offers.
Sierra Trading Post (website) is another option. It's not just workwear and outdoor gear, but also a lot of mid- to high-end brands, with a fair amount that's made in the USA. Sign up for their daily email specials. It's a bit of a gamble, and after a while you get a feel of what specials are worth taking advantage of. When a made-in-Canada Viyella or made-in-the-USA Gitman Brothers shirt that's $150 retail is listed at a sale price of $50, and you get a "45% off 6,000 items" coupon that day that applies to it, it's time to pull the trigger. They seem to have a lot of Hickey Freeman (made in the USA) and Jack Victor (made in Canada) suits.