Dell and HP's look good on Paper
but I'm suspect on the quality control, and easy of use when it comes to getting things properly calibrated.
Because a glossy display is a non-starter for me the Apple displays were right out (also I don't like the 16x9 aspect ratio of the 27" for photo editing, much prefer the 16x10 aspect ratio of the 30")... so I looked really hard at the HP and then got really excited when I saw Dell release the new updated 30" display.
But in reading the reviews for both HP and Dell monitors it was clear that while they display a lot of colors they don't do it nearly as accurately as some higher end displays and can be a real pain to calibrate and get set exactly right.
So for me I ended up buying the 30" NEC monitor (LCD3090W-BK-SV) as it's both a LOT more color accurate but it's also quite easy to calibrate (simply attach the supplied colorimeter which is customized for the NEC display). I ended up paying a lot more than the 30" Dell or the 30" HP was initially looking at, but I need something that is pretty darn accurate with regards to color and easy to calibrate (something that I'll need to do at least once a month). Granted it's not as sexy looking at the Apple display and lacks DisplayPort and I was less than happy to pay more but I knew the NEC was the right choice.
If you just want a big screen that looks *pretty good* the Dell and HP are fine, but if your a photographer or graphics professional take a long hard look at the reviews around color accuracy, brightness and quality control (lots and lots of people complained about the earlier 30" dell as having color cast images on portions of the screen with Dell saying that was to be expected)