I used to reuse the glass jars, but now I am IN LOVE with the new containers that off-brand baby food comes in. They're the little applesauce cups, but with lids!
They're much easier to fill because of the wide opening, the lids are much easier to get on and off, and they stack SO MUCH BETTER than the glass. Especially in the freezer. And you don't have to worry about the glass breaking if it falls out of the freezer. Which just happens.
The only tricky thing is that you have to be careful when you're opening them for the first time. If you peel the foil back very carefully and slowly, you can get all the foil off. I have several that still have pieces of foil stuck to the rims. This actually doesn't cause problems in my microwave, but I was visiting my friend and used her microwave, and there's a little black mark next to the foil now. Didn't ruin anything, though.
I also use some containers that I found at Dollar Tree on the baby aisle. They're 6 for $1 and come in blue, green, yellow, and red, i think. I found them when my first was a baby (now he's 6) and they still have them, although as with anything in that store, they are sometimes out of stock for long stretches.
BTW, the rectangular Gerber containers do not seal. I don't know why they even make lids for them, because once you peel the foil off, you can never seal them again. So don't get duped into buying those for the containers!
P.S. I HATE HATE HATE freezing in ice cube trays. Maybe it's because my kids have enormous appetites. They'd eat 10 cubes per meal. It's very cumbersome to get 10 cubes into a serving dish and microwave them. Instead, I just grab a container from the freezer and put it in the fridge to thaw. When I take it from the fridge to feed the baby, I get another one down from the fridge, etc.