As we all know, Android caches the hierarchy of items in our SD cards. This makes applications like the Gallery, etc run faster but it also becomes a problem when we use applications like EStrongs File Explorer to move around files/pictures on our SD cards.
So far the only way really dscussed to have the phone "Re-prepare the SD Card" is to either connect the phone to a computer in Disk Drive mode or to restart the phone entirely.
I found the widget Reload SD in the Market which forces our phones to "Prepare the SD Card" and re-load the cache...
http://www.appbrain.com/app/com.theta.droid
This saves me tons of time and is a prayer answered... [-o<
EDIT: Please note this will not re-mount an unmounted SD Card