I was just surfing eBay and came upon this: a guy offering a $50 T-Mobile To Go refill card, or rather PIN, for $41. That's 18% off the normal price!
CheapPhoneCards is a good place to find cards for below retail all the time, but they would charge $45.13 for this card (witht he refill5 coupon code). Yes, you get about $1.29 worth or reward points with it but that's still $43.84 net. So you're saving a pretty significant amount by buying from this guy.
I just asked the seller and he accepts PayPal so if anyone has a T-Mobile To Go phone this is a pretty good deal.