i have a Dell 24" wide screen, and i have no regrets about it in the slightest. people think it's a TV.
JonSarik is correct that the same "size" in a widescreen has less vewable area; this is because monitor sizes are measured on the diagonal.
however, i assume if you're debating this and asking this question, you might have some money to spend. the 24" Dells are going for less than $700. Dell sucks on most accounts, but they make damn fine LCDs.
with a driver download, it'll work in portrait or landscape mode. i have my Dell monitor at work in portrait because it allows me to keep two open windows on my desktop; handy for jumping between apps when you need info from both. Dell also adds 4 USB ports and 2 multi-media card readers standard on their newer monitors - a very nice perk IMO.
i wouldn't recommend the 30". they're very expensive, and their resolution is funky. the 1920x1200 is perfect for most media transmissions. it's about interpolation ratios. TV broadcasts match up to a perfect ratio of 3; standard DVD and most current HDTV (720i/p) line up to a ratio of 2, and 1920x1200 is essentially the next standard for HD broadcasts (ESPN hopes to switch to 1080p by the next football season). the larger size of the 30" monitors creates ratios of non-whole numbers, which leads to interpolation artifacts. see:
this article.now, if you wanted something bigger than a 24", before getting a 30" i'd recommend considering an HDTV. the Sharp Aquos is one of the few TVs on the market that's truly 1080p ready (it comes with 2 HDMI jacks). DVI to HDMI converters are cheap, they shouldn't really compromise data flow, and HDMI cables are a lot smaller and more flexible than DVI cables, which is nice if you want the room to not look like a mess of wires. windows XP MCE should have no problem using one of these puppies as a monitor with an easy update. they run at 1920x1080; i was looking at the 40" model for about $2k, which is cheaper than 30" monitors and only a bit lower quality resolution (i mean seriously, you probably won't even notice those last couple megapixels). and since they're LCD instead of plasma, you can game to your heart's content without feeling like you're sucking up your screen's limited lifespan (and probably do it from your next door neighbor's house).
just my thoughts on the issue. i love gaming, but i bought my system as a home entertainment PC primarily. if you'd like your electronics to work double time, i'd definately recommend a widescreen monitor - it's the standard that'll be here for years to come.