The SPIbelt is our all time favorite pouch for my daughter's pump. Small, low profile, comfortable. We call it her 'speedo' since it's made out of the same material. website is www.spibelt.com. two discount codes: 'bday2010' gives you 15% off OR ship09 is for free shipping.
They've got a special pump belt now that has a separate hole for tubing. I don't bother with those, but just pick from the cool kids designs. Highly recommend this for active kids on pumps.