Jon and my parents have both asked me about a simple phone that isn't complicated or smart like an iPhone or a Blackberry, my two current recommendations. In looking at this, the main criteria are:
# Big screen. So you can see the numbers you are dialing (most folks at this level won't be using an address book)
# Big keys. So you can type easily. For some folks the Blackberry keys aren't.
# No new chargers. Really want a USB input so you don't need to have separate chargers
# Good reception
# Flip phone so you don't need to have a case and don't hit the keys.
The guy at the AT&T store recommend "phonescoop.com":http://phonescoop.com as a good place to look and he's right. On "T-mobile":http://www.phonescoop.com/carriers/carrier.php?c=5 they sort reviews by carrier.
Looks like the best bet is the "Motorola W490":