As a layman, I find this software a bit amazing. Apparently it's not safe to sell or give away old memory cards, depending upon who or what you've been shooting... 
http://www.macworld.com/article/140290/2009/06/klix.html?lsrc=nl_mwgems_h_crawl
My friend in need:
" desperate for ideas. I moved my vacation pics from my camera to a Flash Drive, deleted them from my camera and then accidentally deleted some of them from the Flash Drive
. I immediately tried to recover them from the recycle bin, but they weren't there. Is there ANY way to get them back without having to pay for recovery software? Help!"
anyone? Bueller? Bueller?
OK first I've NEVER tried this but here is a free program that says it will work on Flash Drives - again never tried it: clicky
if you try it let us know if it works

Thank you I let her know your ideas 
Recuva is my secret weapon at work. When a nurse accidentally deletes a patients photo after the patient has left or when cards go bad. It's made by the people who make CCleaner.
http://www.piriform.com/recuva
I use advanced mode and it works like a champ. The most important thing to remember is to stop adding new data. That means install Recuva to a Flash Drive or secondary HD. Every bit of new data overwrites some old data. Once you've damaged it enough the free programs won't cut it.

Wellington Florida
Married
Well even old computers the hard drives can have the data recovered. There are lots of companies and programs that recover data, google "data recovery" and you will see. Its scary you can give away all of your personal data and not even know it. That is why I recommend pulling hard drives and getting a external case and keeping them. As for old memory cards - if you want to trash them then make sure there is nothing they can get off of them. Drill holes into the card or drop it in some acid - poof card is destroyed.