MBP Adding Another DVI Monitor

Right now I have a 22.1in monitor hooked up using the DVI connection on my MBP. Is there another way to add another monitor? I've seen a few products such as

http://sewelldirect.com/vtbookpcmciacard.asp which seems like that would work, but is pretty expensive.

http://sewelldirect.com/USB-to-DVI-A...1600x1200.asp# this guy is PC only the moment.

http://www.cablesunlimited.com/produ...roupcode=I3581 what about a DVI splitter? Would that do the trick?

Any other suggestions? Thanks.