I like Pyrex, because glass is a nice material to eat out of, and it's microwaveable. But it is heavy. These containers have a terrific seal on them. For containers that might leak, I'll put plastic wrap under the lid and then secure that with rubber bands. Then I'll wrap the container in one or two plastic grocery bags. I'm concerned about the long term effect of eating food wrapped in plastic, so I prefer my food contact plastic for as little time as possible. Heating food in the microwave while still in plastic seems particularly scary.

I've also bought glass containers at the local Chinese grocery store, and they look like lock-n-lock that @BikingZombie mentions. If you have a local Asian supermarket, you should go. The food is excellent, and they normally have a fantastic kitchenware section with super prices.