Anyone where I can go to create flash banner ads?

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I'm fairly new to this making money online. I have created a website, but I've looked high and low for software or websites to go where I can create banner ads for my website to advertise. If my website program offers this service, I've haven't been able to find where it's at. I'm looking for the banner ads for traffic exchanges or to place on others websites so I'd need to be able to make different sizes. Any suggestions?