I'm working as a TA now, and I've found that I'm spending an inordinate amount of time on my TA-ship. Is this normal? Furthermore, is this expected? I'm worried that my research career will suffer because of my lack of research productivity.
I suppose it depends on the factors that are causing you to spend more time teaching than you think you should. You should talk to (1) the other TAs and (2) the course leader/director. Find out what is expected and what others are doing.
If you are a relatively new graduate student, then I think it's normal to spend more time teaching and preparing for your teaching. As you start teaching the same courses repeatedly, the time you have to spend in preparation will decrease.
If you think of the time you are teaching as working on a craft that you will use for the rest of your career, then it is time well spent.