Pyrex rocks the house. It's durable, affordable, and you can find it anywhere. At a minimum you want a lidded casserole dish, either glass or ceramic, and a rectangular glass baking dish, like you would make lasagna in. No lids come with these but they are easily covered with foil if necessary. I use my Pyrex bakers for the aforementioned lasagna, roasting veggies, making cobblers, roasting chicken parts, baking fish, etc etc. If it's within your budget get two different size casseroles and two different size baking dishes, so you can cook more than one thing at a time.

If you think you will be doing a lot of large things like whole chickens or roast beef you can get the metal roaster, but otherwise don't bother until you specifically have a need for it.