Becca,
I use my memory, but that's easier for me, because I cut almost all of my own blanks (or have a friend help me). I did get two woods mixed up once, but I sorted it out. Please post some close-up pics and maybe we can help you. I study the woods when they come in, or have studied them previously, so I can tell them apart. Some woods I have never dealt with, but someone else here most likely has. There are a lot of smart cookies here.
Also, you can ask your supplier to mark the blanks for you. If you get the order in and have ordered them in groups, you may be able to separate them and label them then, before they go on a shelf. I line mine up on shelves and mark the bottome one with an initial. Of course, I have about 50 types of wood, so I have found that it is easier to mark them, than to remembere what they look like. Also, some woods have more than one appearance. For example, Honduras Rosewood can be very light, medium brown, dark, or a mixture. You may also have some figured, or alternatively-cut woods, like cross-cut, etc. If you can't tell them apart, you may want to mark them too. It's my least favorite part of selling blanks, but it helps out the turner.
Rob