MacBook Ability to run external monitor

I have a SR mid range MacBook purchased in early November. I decided to see if I like the dual monitor setup by hooking it up to an older dell 17" monitor that I have. After using it for a few weeks I have decided to purchase a better monitor.

I have two options. I can take the 19" dell monitor that I use on my main PC and use that with the MacBook and buy new for the PC, or I can purchase something to use with the MacBook which I would prefer.

Since I am new to the world of Macs, how can I determine the size of monitor that the MacBook will support up to. I gather for example that a 30" is too big, so is 23/24 my best bet, or is even that too large. I have followed all the discussions about ACD vs other Manufacturers, but I couldn't find anything relating specifically to size.

Thanks
Susanne