Sequitur: I use mine every day, from Movie/MP3 transfers to take to school, to daily notetaking, so stuff gets added/removed from my Viking 128Mb very frequently. It's been running perfectly. I don't know if all SD cards have this, because I haven't worked with them since I got my Ax, and these are the only ones we own, but there is a lock switch on them to lock all the data from deletion/modification. Nice feature if you have multiple cards and want to make sure you don't accidently delete something important. Again, all SD cards might have this feature, I'm not sure.
I got ours off of Amazon.com... they ran a deal where it was 50% off all SD and CF cards. I went with SD instead of CF simply because of our wireless CF cards, they usually occupy the CF slot.
This is a link to the card... it should work for you... although it's a page I was on while I was logged in, but I think it'll still show you the product...
http://www.amazon.com/exec/obidos/AS...877096-4988614