DVDSoon is usually better than Amazon or Indigo.ca for prices, although they do tend to package things poorly from time to time. (They occasionally stuff things into envelopes that really ought to be boxed, although if you pay them extra they will box it.) Some of their prices are good, but some are just plain hideous. It pays to check around for every title. Most of the Canadian etailers are usually in the same ballpark, but on some DVD's you'll get a much better deal ordering from the states. (e.g. I often order Criterions from U.S. sites.)
DeepDiscountDVD is the american site I use the most. Their prices are usually very good for a U.S. site, but they also have good shipping rates. (Some U.S. sites will soak you big-time for daring to not live in the center of the known universe!) You will get hit with duties at the border but the price differences are often large enough that you often come out ahead. (depending on the exchange rate)
Take the following prices on Criterion's edition of Spartacus for example:
- DVDPassion - $61.00
- DVDSoon - $54.98
- Amazon.ca - $63.98
- Indigo.ca - $79.98

- Futureshop.ca - $70.99
- DeepDiscountDVD - $47.62 ($35.96 USD)
In this case I'd go with DVDSoon. With free shipping and no duties they'll probably wind up cheaper than DeepDiscountDVD, although it's close in this case. None of the other stores are even in the running. Always check around though, because the picture can look very different depending on the title.