Shower combs are the ones that come with that hook on them so that you can hang them from something in the shower.
After having spent over $100 on combs ALONE (don't say it, I already know), my best advice to you is to go pick up a good wide tooth rake like the lower pic in WantLongHair25's post, or a nice $2 Jilbere shower comb that everyone keeps talking about. When it comes to combs, the simpler and less expensive -- the better.
I have owned horn, plastic, bone (yes the real ones), and those clear acrylic types. Get yourself a full-size plastic comb with wide teeth, round teeth if you can find them. If it has seams, get a 400/600 grit nail file from Sally's and file the seams yourself.
Horn is not properly smooth, neither is bone IMO, so they both strip without it being all that noticeable until its too late. Acrylic snaps too easily. And forget about those little bitty ones altogether. They're toys!
But if you decide that you absolutely HAVE to try the horn or bone ones (don't do it girl!) then you can PM me. I still have them. I'll throw them out when I've owned them long enough to not feel bad about having spent so much on them.
End rant. Hope that offers some guidance.