I may get my hands on a Amazon.com bought Playstation Plus code. And was wondering if this is redeemable outside the US?
This all depends on what region you bought your code from and what region your PSN account is. If you bought your code from Amazon.com (as opposed to say, Amazon.co.uk/Amazon.de/etc.), then it will be only be redeemable on a North American account, not a European one.
I live in the EU and have European PS3. However, my PSN account is North American, so I can redeem North American codes even though I am physically located in the EU. If you had an EU account on a North American PS3, you'd still only be able to redeem codes that were intended for EU accounts, not NA accounts.
Everything depends on what region your PSN account is set to. If you purchased the code from Amazon.com, then you should be able to use it on a NA account without any problems.