Adafruit are currently selling a variety of LCD screens for the Raspberry Pi. I received this unit for Christmas, a 3.5" 480x320 resistive touch LCD that mounts on top of the Pi. I plonked it onto the Pi and booted the Pi up ... and got nothing but a bright white screen. So ... not plug-and-play. In fact, you have to use a custom-built image or run a script on your already installed Raspbian that makes major changes, all the way down to the level (I assume it's an Adafruit kernel, I haven't confirmed that) that the start-up logo right after GRUB is now a starfruit (Adafruit's symbol) right next to the Raspbian Raspberry. I'm not particularly pleased about that, but not too surprised either. I hope support will be mainlined into the kernel, but I'm not holding my breath.
Is it worth it, is it a good investment? I'm giving it a qualified "yes:" it's exactly as advertised, and both surprisingly readable and nice-looking. The screen refreshes VERY slowly (text ripples as it scrolls on the console) and you'll need a stylus of some sort since the screen is too small for my fat fingers, but yeah, I'm very happy with it.