Photoshop Creative

I have been looking at new SD card for my Nikon D40. I have a SanDisk Estreme III that I use now. I have noticed different numbers on the card when doing some online shopping some of them have a 10 and some have a 6. the one I have now is a 6 and says SD HC. I was wondering what is the difference and what card should I be looking for. The one I have works fine but I want larger than 4gb and as long as I am spending money I want to get the best for my dollar.
Can anyone suggest or explain what to get?
Tina B

Tina,

Not sure, can you post a shot of the card?

Or might be this?

Hey this helps , Thanks
Tina B