amazon/buy.com credit cards

[buckshot]

i'm always looking to get what I can for as little money as possible. i never had much money growing up so it was a way to get by. I see that buy.com and amazon.com both have their own credit cards that when you sign up you get $30 off your first purchase. I have awesome credit so i'm sure I could get them both. but my question is are there any recurring charges for these cards? annual fees etc? or could I, in theory, get these cards, make a a $35 purchase on each, pay off the $5 on each and then just leave them alone? I wouldn't mind getting BBC's planet earth on blu-ray for around $40 from amazon and both terminator movies from buy.com for $5. would that work?