I know this is a bit old of a topic... but... don't jump on me.
Frequently I use laptops with the internal monitor open + an external monitor, giving the semblance of dual monitors.
I did try the Dell with Dock with dual port PCI card. It crashed something... I don't remember what, but I ended up re-imaging.
However, The IBM/Lenovo/Thinkpad "Advanced Dock" supports a full PCI-Express Slot.
Somewhere I saw an article about running the Advanced Dock with Quad Monitors.
I believe that it could also be cobbled together with the Dell 30" Monitor to provide truly spectacular graphics (I haven't tested it, but theoretically it should work).
Check out the articles:
http://forumserver.twoplustwo.com/showflat.php?Cat=0&Number=7429843&Main=7407680
http://www.tradersworld.com/computers/ThinkpadT60pwithAdvancedDockingStation1.htm
Oh,
There are also some PCMCIA Adapters that you could look at. But, personally, I'd go for a native dock solution.
http://www.digitaltigers.com/sidecar-fxelite.shtml
And, of course,
The Apple MacBook Pro's all support the Apple 30" Cinema Displays.