Just to keep things up to date: with the Hilton Platinum AMEX card, you can now get
five points/$ at supermarkets, gas stations, drug stores, and when paying for wireless phone bills.
I got my Hilton AMEX a little over a year ago, and got a second one (free) for my wife, since she does most of the grocery shopping. I run a lot of stuff through that card, and I think I've netted about 100,000 points with ordinary spending since I've received it. Not bad at all.
In addition, if you spend $20K/year or more through the card, you get an automatic Hilton Gold elite status for the next year. The rumor is that if you spend $50K, you get Diamond, but I've yet to see that confirmed.