As with most things, it's going to come down to how much money you're willing to spend, because where monitors are concerned, higher-quality panels offer noticeable differences. But, it also depends on how fussy you are, because in all honesty, even $250 24" monitors offer good quality, such as the one reviewed here. You can read more about this monitor in
another thread, and read
2Tired2Tango's thoughts as well, since he just purchased one.
I personally like Dell's 24", and I'm very pleased with the 2408WFP, but Samsung also makes some stellar displays as well, for really good prices. As for this ASUS, I can't really comment on it since I haven't seen it myself, but it received a good review here, and 2Tired is thrilled with his, so I'd say it'd have to be a good buy.
Also, in a 24", you aren't going to get a 4:3 ratio, unless you want to go purchase an old-school LCD or CRT display. Everything is widescreen nowadays, so finding anything close to 4:3 is going to become increasingly tougher.