The i60 is kinda like a poor mans version of the i90.
I've used both now, so I'm relatively familar with both phones.

Both have a nice phone book feature where you can
assign multiple names to each contact.  Both have
internet accesses (with the right calling plan).  Both
have the ability to set different rings tones, lock the
keypad, backlight, Vibrate instead of ring, headset jack,
yada, yada, yada... the basics you'd expect with most
cellphones these days.

The i90 has the following features that the i60 does
not have:

Java -- Load apps and games on your device.
Advanced Ring Tones -- the i60 gives you 9
   standard tones, the i90 has those plus allows you
   to add more
Datebook -- the i90 has a simple date book
Cutomize able menu -- the i90 lets you put the menu
   funtions in the order you want.
Voice Dialing -- you can program the phone to dial
   numbers when you speak the right name (you need
   to hold down a button for about a second to activate
   this function.
Preview Window -- as you mentioned, it's got the
   little window in the front.
Voice Recording -- Record a few seconds.

Those are the things I know about/use on the i90.  I
imagine there maybe a few other items that others
could tell you, but those are the basics I think.

       Chris