dansgil said:
Personally, I want a CHEAPER 20" display. It doesn't have to be in an aluminum enclosure, or even have a USB/Firewire hub, just cheaper.
Dude, you're getting a Dell!

Seriously, if you don't care about the enclosure, get a Dell 20" WS. Better screen than Apple's (or at least as good), more inputs, more extra features, half the price.
Anyways, I voted for a 4th LCD, but not a big one (between 23 and 30). As noted, they need a 17" LCD. Widescreen would be cool, since there aren't many of them on the market they could justify the price premium. Don't do it in alum, both to keep costs down and to help keep it from stealing sales from the 20" (which, let's face it, if you are buying it's for the looks - there are better options out there).
Ideal: 17" WS, 1440x900 (iMac 17" panel) in an iPod styled enclosure with DVI and VGA input. Four port USB2 powered hub. $249. Other options: built in iSight, optional BT2 module (connects over the USB bus) would be kinda neat, bundle with keyboard and Mighty Mouse (mini add on bundle).
If they did a bundle with a keyb/mouse for $299, you could get a mini WITH display, keyb and mouse for $900. Run a promo and give away a 1gb shuffle to anyone buying a mini+monitor+keyb+mouse bundle and you would have the ulimate switcher bait... complete computer (s'pose they need to toss some speakers in there) with display AND an iPod for under a $1000 with tax.