The short answer with respect to oxygenation is any freshwater plants will do this.
To explain... the oxygen from this presence is a natural byproduct of the photosynthesis and for a plant submerged in the water, it's only going to go where you want it to go. However, there are some added advantages to this cycle:
Removal of carbon dioxide from the water.
Hiding place for your fish.
Now, the logical follow-on is, what plants are good with your fish? Since I know you have goldfish and your pond pots are deep, you can get some bigger plants. The primary concern is that goldfish are opportunistic eaters and will nibble at your plants and so bigger, hardier, plants are going to be more likely to survive the fishy assault. Some possibles include:
There's a whole lot more. A quick search with Google for goldfish friendly plants will give you a lot of information. Once you have planted your pots, however, you need to keep an eye on the plants. Goldfish are hard on them and a dead/dying plant can actually be counter-productive to the situation and health of the system. Something to be aware of.