Jos A Bank always has some ridiculous sale on. Bottom line, 2/3 off suits (when you buy 3) is their standard sale - at least 4 times a month. A few times a year, they have a sale that works out to just under 80% off, and you only need to buy 2. One such sale is after Christmas, I can't recall when the other one(s) are. FWIW, the current suit sale is pretty good - much better if you go for hte higher end suits.
On shirts, for the no-iron dress shirts the best sales work out to ~$22/shirt (you have to buy multiples). They are harder to find. More often, you see a sale that works out to ~$30/shirt.
The key things to remember here is that you can always return something with no time limit. So if you buy suits or shirts at full price (as I did with shirts a few weeks ago), just hold on to the receipt and when a big sale comes along you can get a refund for the price difference.