Ok I have 2 goldfish [a black moor and an oranda] I only got them about a month back so they are still small, but they are in a ten gallon tank. I know that you should have 1o gallons+ per fish, and hopefully I will be getting a larger tank for them when they start to get bigger. Is a filter essential?
Before I got the fish I thought I would wait and see if I actually NEEDED the filter, and Ihave been doing weekly water changes of about.. 5o% and the tank looks pretty clean.. should I get a filter anyway?

Yes. A filter will help keep your tank aerated as well as give the good bio bugs a place to colonize. In addition, it will keep you from having to change so much water so often. In a tank as small as a 10 gallon you can easily find a filter at nooppee or a pet store in the $10-$15 range. Definately get one. It will help cut down the work on you and help to keep your fish healthier!