Many cards come with an additional 1 year warranty protection through the CC processor (Mastercard, Visa, AMEX, etc.). I think the general consensus is that the warranty service of AMEX is better to significantly better than the others. I have heard good things about visa signature warranty coverage, but nothing superior to AMEX.
For return protection, cards issued by AMEX (e.g. not a Citi Amex card) come with a 90 day $300/item return protection plan for up to $1000 per year. I have taken advantage of this for an item the merchant wouldn't take back, and it was painless.
Most or all of my electronic purchases are done with one of my AMEX's.