I've bought pets and mounts before, so I think having those in an in-game store just makes sense and I'd like to see more of them. And I have no problem with the other items -- though I doubt I would ever buy any. But there are a couple other things I'd like to see available.
(Note: I wrote this before the transmog helms at the pet store news hit.)
I'd like purely cosmetic gear to be available at the store so that I can dress up my characters in many non-conventional ways. Perhaps they could offer witch sets for warlocks and mages or kung fu sets for monks. These wouldn't affect gameplay at all, and would add an even greater selection of silly (elegant?) fashion choices.
High level alts
This is going to be controversial, but I'd like to see the availability of high level alts for people with max level characters. I enjoy leveling -- I really do. But now that I've taken several alts through the same content, it is getting to be a bit old. Since, except for monks, we don't really learn how to use all of our important skills until the end game and since we'll probably have the Proving Grounds to teach us how to be better players, I see no reason why people should have to level if they don't want to.
Right now, we can spend the money on a second account, use the Scroll of Resurrection, get a level 80 character and then spend the money to transfer the character to our main account. It's roundabout and expensive, but it is possible. Something similar can be done with Recruit a Friend. So it's not like we can't buy ourselves high level alts right now. Why not just offer them for say twice the amount of a character transfer?
This would be good for trying out another class at max level or making one of your favorite class to play on a different server with different friends. The only drawback I see is not knowing how to play the class, but that's happening now anyway with how easy it is to speed-level characters these days.
Would you buy anything from the in-game store? And if so, what? Blog about your answer and link to it in the comments below. Or if you don't have a WoW-related blog, just leave a comment with your response.