Id use ebay. Ebay is almost always the cheapest place for memory. ebay has 16gb cards for $49 (cheapest price on ebay)with free shipping. Name brand too.
yeah I know the storm comes stock with 8gb, unless i am mistaken and there was a 16gb option available, due to storm being the one that was trying to be the iphone killer, it wouldn't surprise me, Heard via WES that samsung just cut a 32 gb one. and I believe the storm, or mebbe the bold -_- should support it.