According to wikipedia, "Sales taxes are assessed by every
state except Alaska, Delaware, Montana, New Hampshire and Oregon". I believe California and Washington state have some of the highest sales taxes - around 9%. If you live fairly close to the border with one of these "sales tax free" states and don't have any friends/relatives living there, I would look for a shipping/receiving business whose address you can use for delivery purposes. When the package in delivered they will sign for it and hold it until you pick it up. I believe it could be really worthwhile - especially if you are spending thousands of dollars. After all, 9% on $10,000 is $900.
As I mentioned previously, Canadians who live close to the border with the USA can save huge amounts of money (on certain items) by shopping in the USA. For example, let's take a look at Hermes pricing - in Vancouver, a GM shawl is $1,375 Cdn +12% tax (total $1,540 Cdn or $1,468 USD), while the same shawl can be purchased on hermes.com, shipped to an address in Washington state for $950 + $30 shipping =>total $980 USD vs. $1,468 USD in Vancouver. That is a huge price difference.
By the way, I just made some interesting calcualtions - here are the prices (from hermes.com) in euros (I used today's exchange rate on finance.yahoo.com) for a 90 cm carre:
USA - 248 euros
UK - 251 euros
Canada - 268 euros
France - 275 euros
Australia - 323 euros
While the price difference on a 90 cm carre is not that much, it is much more substantial on other items as per my previous calculations.