I would go for one 30". I feel this gives more flexibility than two 23-24" screens. With a 30" you could have one 1280x1600 area for the main application (in this case the code), and maybe two 1280x800 areas for docs. Or (the way I usually set it up) you could have one 1536x1600 and one 1024x1600 area (or two 1024x800), or any other variation that's suitable. I feel this added flexibility negates the 12.5% pixel advantage of 2x24". Also the 30" is much nicer if you ever need to do something besides coding, like working with timelines. Also I feel 1920 pixels isn't quite enough to put two windows side by side, though I guess it could be passable for docs.
Though I must admit that having one 24" rotated to 1200x1920 is pretty nice, as long as it doesn't get too narrow. Personally I would probably still go for the 30", but it's a close call.