what supplements if any should I take when I become a vegetarian?

If you eat really well, you don't need any supplements.

the one vitamin that always comes up is b12.

Personally I believe a decent multivitamin is like an insurance policy, so just take one that has some b12.

the other thing is that if you don't eat fish, then the omegas might be an issue. Its complicated but from what i understand being a vegetarian actually changes the requirements of omegas and that a little ground flax seed in your morning smoothie should take care of it.

Of course every non vegetarian is going to tell you that protein is an issue. but it's not. But if you are worried about it a small amount of soy protein powder a day won't hurt.

if you like podcasts, the compassionate cooks podcast has a very good "episode" on supplements worth listening to.

none animals get all the vitamins they need without meat and only eating fruit and vegetables if they can why cant u