Sangy has pretty much covered the different types of SD cards in use today. I have resurrected SDHC cards in the past via formatting in a Nokia E63 phone! Yep! That's the ONLY way I was able to save the 8 GB card! Windows would not even recognize it. Even RMPrepUSB (a great formatting program to use on USB/flash drives) would not recognize it. But my old cell phone would! And, it formatted it with no problem to boot!!!
I NEVER, NEVER throw away any old phones. When I bought my new iPhone (which I really couldn't live without), I replaced a Nokia E63 (a problematic phone) and a Samsung Blackjack. Both of these phones accept SDHC cards. So I use them instead of buying a memory card reader. I do have a memory card reader but, like Sangy above posted, it doesn't read anything with over 2 GB of memory. Enter the old phones to the rescue. Don't throw away those old phones!
I hope this helps...