I use a CompactFlash card for my DSLR camera (I've had it for several years, so yes I know how to operate ;-)
A month or so ago, I took about 100 photos. I downloaded them to my computer, but left them on the card since I had not burned a hard copy. Today, I took several photos (and viewed them on the camera after taking... even scrolled through to look back... and they were there) and when I went to download the images, they are not on the card. The card is not full, and the camera never gave any sort of error message that photos were not stored or anything of that nature. And now when I put the card back into the camera, the images do not show (as they had earlier in the day).

I am so confused and have no idea what could have happened or what I can do to retrieve them!

Please help :-)

Is it possible you stored them on the onboard memory instead of the card? Also when is the last time you did a complete format from scratch for your card? It could be cluttered.