What resolution are you looking for 'cause some 24" LCDs are 1920 x 1200 while others ar 1920 x 1080. I've read a few post where people disliked using a 1920 x 1080 because the width is too narrow than what they are used to. I can understand the point since I too prefer 1920 x 1200 over 1920 x 1080 resolution.
Additionally, I would avoid LCD monitors that are built around TN panel since they have poor viewing angles which can affect colors displayed on the screen. You want MVA, PVA, or IPS panel tech since they produce much less color shifting issues than TN panels. What monitors uses which panel tech? It's difficult for a noobie to know so post the model you are interested in and individuals like myself who have spent several hundreds of hours doing research over the course of a few or several years on LCD monitors in general.
The Samsung BX2440X uses a TN panel. A dead giveaway is the price and viewing angles of less than 178/178 (vertical/horizontal).
To give you an idea of what types of images a TN panel can provide see the below picture from a Samsung P2450H:
Lovely colors right? What you see is actually a bit better than average for a TN panel.
Here's the review:
http://www.prad.de/en/monitore/review/2010/review-samsung-p2450h-part6.html#Viewing
Here's what the NEC EA231WMi looks like. This monitor uses an e-IPS panel which is an "economical" version of the standard (and more expensive) IPS panel. It's resolution is 1920 x 1080:
While the image is different from the one above, the thing that should strike you the most is that the colors are more consistant. This is an absolute important factor when considering using a monitor in portrait mode.
Here's the review:
http://www.prad.de/en/monitore/review/2009/review-nec-ea231wmi-bk-part6.html#Viewing
Of several monitors mentioned in this thread I recommend the HP ZR24w because of the following reasons:
1. It uses an e-IPS panel
2. Because of #1, it is relatively inexpensive at approximately $400
3. Resolution is 1920 x 1200, or 1200 x 1920 in portrait mode. I think you will appreciate the extra 120 columns of pixels.
4. If you were to play games it only has an input lag of 10ms.
*
* Input lag refer to the delay between the time you press a key, move the mouse, click the mouse and when that action is registered on the screen. This is measure in milliseconds (ms) or thousandth of a second. 16.67ms = 1 frame of lag. This is really only important in games 'cause a "blink of an eye" delay can possibly mean living or dying in a first person shooter. Strategy games, card games, games like the Sims 3, input doesn't really affect gameplay since they are not dependent on lightning fast reflexes. In my opinion 16ms - 32ms is considered good enough for the average gamer. Hardcore gamers and competition gamers wants as close to 0ms lag as possible. 10ms is considered pretty fast for an IPS panel.
Here's a sample of the viewing angles:
Here is the review:
http://www.tftcentral.co.uk/reviews/hp_zr24w.htm
The Dell U2410 is also a good monitor, but it is probably a bit too much than you want to spend. I think it generally sells for $600, but every now and then Dell has a sale on it for maybe $500. Here the review:
http://www.tftcentral.co.uk/reviews/dell_u2410.htm