Suggestions for Multiple 24" LED Cinema Displays and MacBook Pro
I've looked into this in the past, and from what I know, you have a few options:


I'd never really recommend it, you can get a usb adaptor that essentially adds another display port to your computer.  Make sure the one you pick is Mac compatible - there are some that exist.
DualHead2Go is an interesting product that emulates a single double-wide monitor to your computer.  There are some catches:


There is a maximum resolution the device supports
It works best if the monitors are the same dimensions and resolution
It's currently ~$230
The computer doesn't see the monitors separately, which means that when you configure/use it, it will act accordingly.  If you put the menubar on the external 'monitor,' it will stretch across both; maximized windows will be two monitors wide etc.

I can't find anything to back it up at the moment, but at one point I do believe I saw an ExpressPort/34 video card or a breakout box for a PCI card.  The only thing I can find now is XGP, but I'm near certain I saw a Mac-specific solution at one point.


Each has its benefits and drawbacks.  If you're not on a tight budget and your monitors will work for it, I'd recommend the DualHead2Go.