Depends upon what you want. Sony Ericsson T610 has all the features including Bluetooth and infrared, but others have reported that the reception on this phone isn't that great. (If you're at all interested in the phone's built-in camera, this one is weaker than others as well.)

Nokia's 3650 gives you all the same features plus much better reception (and a VGA-resolution camera), but the phone is kinda big, it has the silly rotary button layout, plus the screen doesn't support as many colors (so not as nice to look at). If T-Mobile would get off their a**es and add the 6600, you'd have the same features as 3650 with better screen and traditional layout, plus a bit smaller. These "Series60" Nokia models (and I gather the T610 too) have a fair amount of organizer-type functions. They can sync calendars, contacts and other stuff from phone to computer and vice-versa.

If you like your Moto and don't need Bluetooth or IR you can get a Moto V300. Unlike the other two this keeps the flip phone form factor you're used to. Has a high-quality color screen and VGA-rez camera. Keep in mind this phone is blue. If T-Mobile wold get off their a**es and add the V600, you'd get a similar phone that's not blue and also adds Bluetooth if I recall correctly. I don't think these have as many organizer functions.

You can also settle for a basic candy bar Nokia 6610 which has a color screen and IR, no Bluetooth and no camera. Cheap, basic, should be good reception at least. (I have no idea on this particular model but in general the Nokias have been good.)

T-Mobile's phone selection, in a word, sucks.

Personally I have a 3650.