This one from mini-box should do it. http://www.mini-box.com/DCDC-USB If you need more than 10 amps, you're into some specialization.
I'm looking to put a Linksys NSLU2 and 2 powered usb hubs into my car, can anyone recommend a 5v output psu that would be up to the job?
Can you recommend something that has 3 5v outputs that can handle up to 5A?
5A per output? or 5A total?
If all of the parts are going to be turned on and off at the same time, you only need one output. Just split the output yourself into however many 5V feeds you need.
You can do it either by tapping one main line with as many branches as you need (include fuses as required), or you can set yourself up a nifty little distribution block that you can add or remove lines from as your situation changes (Again, include fuses as required!).
So while the DCDC has only one output, you can split that one output to as many devices as you want, as long as the total power draw is under 10A, which for an NSLU2 and a couple of hubs with devices attached, should be pretty easy