If a buy a mac from another retailer, do I get the same warranty that I would get from Apple?

On this page, it shows that without the Apple Care package, you get 1 year limited warranty, and 90 days of complimentary telephone technical support on a mac.

If I buy the mac from another retailer (e.g. Amazon), would I still get these same benefits?

You'll get the same warranty from an authorized Apple retailer as you would from Apple directly. I don't know how prevalent it is today, but for a while you could buy refurbished Macs from non-authorized retailers and you ended up with little or no warranty. (Note that Apple sometimes sells refurbished machines that do have full warranties; the warranty's existence is dependent upon the authorization status of the retailer.)

Apple provides a way to determine which retailers are authorized on the Solution Professionals portion of their website. Be sure to check that list before making a purchase.

Every new Mac comes with 1 year of AppleCare. The option is to extend that AppleCare up to 3 years. And, I believe you can do this at any time, IF the Mac is STILL covered by your original 1-year. As in - I believe you can buy 2 extra years right before your 1 year (that it came with) is up.

With regards to a warranty done by "in house" staff (IE - FutureShop or BestBuy selling you one of "their" warranties, which are supposed to be better), it's usually not worth it. They usually end up sending your stuff off to Apple to fix, so you just wait longer.