I shop Hugo Boss (my favorite), Club Monaco, and French Connection.
Stick with actually going to the boutiques to get your clothes. The reason why is because they have the best selection and newest styles.
For example, I checked out Nordstroms Hugo Boss collection, it is quite limited in selection.
The key is to find out when the boutiques have their sales. They usually hold sales after the season is 1/2 way to 3/4 over. If your size is common (as in, not small) then you will definitely be able to find something in your size. The Club Monaco sales rack is a gem, as you usually find clothes discounted heavily. French Connection is the same.
Hugo Boss (at least the Chicago one) has ridiculous sales when the season is almost over (40% or so).
On the other hand, you wear a hard to find size, like small for shirts, or 31 pants for Hugo Boss, then you are better off just paying full price, because by the time the sales come, your size will be gone.
Also - be very *picky* when it comes to buying designer clothes. Many of their clothes look just like their cheaper counterparts at say Gap. If that's the case, you are better off just buying the cheaper knock-off.