No i haven't heard of Amex's serve but some good alternatives are the following :
- Moneybookers
- Alertpay
- WesternUnion
- Moneypak
Thats all i know, glad to be of help if i was.
Have you ever used PlayerAuctions? I used that as an alternative - it's slightly safer than Paypal on its own (you use methods like Paypal to purchase) and confirmation has to be given on delivery. As long as you video your trades you shouldn't lose much.
Serve is alright, it's just fairly unpopular and requires a relatively high amount of personal information to activate an account. I personally recommend playerauctions
Playerauctions. That or w/u are the best methods IMHO, as cash can get lost in the mail (unless it's tracked), and moneypak is pretty safe also I've heard.