What hardware needed for multiple monitors (3) on a 2009 MacBook Pro 5,5 with displayport (NVIDIA GeForce 9400M video card)
A new product has been announced today about this. On the Windows side, the Matrox DualHead/TripleHead were common, but not available for Mac. 

That has recently changed because Matrox Introduces New Mac-Friendly DualHead2Go DP and TripleHead2Go DP Multi-Monitor Adapters.