MacBook – What hardware needed for multiple monitors (3) on a 2009 MacBook Pro 5,5 with displayport (NVIDIA GeForce 9400M video card)

I am adding a 30" monitor to my existing setup (a 24" monitor) for use with a 2009 13" MacBook Pro 5,5 with DisplayPort. This is the model with the NVIDIA GeForce 9400M video card. This MacBook Pro should support the higher resolution of the 30 inch model (2500×1600 res), but…

How do I add the older 24" monitor (1900×1200 res) into the mix?

The laptop stays closed, but technically this is 3 screens. The older monitor only supports DVI and VGA inputs. I have read about several USB to DVI converters on Amazon, most with mixed reviews.

Can anyone recommend a specific piece of hardware known to work?

Later addition:

Thanks everyone for the helpful answers.

Thanks Martin, but the Matrox is unsuitable for my setup as I have one 2500×1600 and one 1900×1200 monitor. The Matrox website says "maximum resolutions of dual 1920×1200 and triple 1360×768 under Mac" and I've read elsewhere that both resolutions need to be the same.

John, Thanks for the tips – that is indeed what I settled on; a Kensington USB to DVI Converter (with DisplayLink 195 chipset).

My additions to your suggestions:

1. Definitely use the latest drivers, even if beta. I had a major problems with the DisplayLink 1.5 drivers when trying to resume from sleep. The 1.6b3 drivers fixed that.

2. You cannot use the Mac built in screen capture on the USB monitor. No biggie, but it tripped me up until I figure out that was the issue.

Rock on.