Based on several years experience optimizing Internet ad campaigns, here are a few banner advertising tips:
1. Test and track EVERYTHING. Every variation, headline,layout, domain ad is on, etc should have a unique ID, so you can see not just what gets the highest CTR but also which ad converts/backs out the best.
2. Good design does not necessarily mean good ads. I've had the highest CTR and conversions come from the simplest, ugliest ads. See Plenty of Fish banner ads for an example of ugly,yet effective advertising.
3. Regardless of the direction you take your design, have a clear, easy to see call to action ("click here!" button for example). Design the ad to draw the eye towards that button.
4. There are two main strategies in banner ad design, blend or clash. Either blend in with the design of the site your banner appears on with similar colors and visual elements, or go the other direction and make an ad that clashes with it and stands out.
More specific banner media buying advice:
Taget smaller sites your customers are likely to visit. Ask to buy remnant inventory, and pay CPM. Don't pay more than $2-$3 CPM except in specialized cases. Don't go through ad ad network unless you have a big testing budget, instead go direct to webmasters. Use your own adserver and pay based on your adserver's numbers, not theirs. 1% CTR is fantastic for banner ads, but your EPC/conversion numbers will be the way to determine if an ad is succesful.
My email is in my profile, you(or anyone else here) can email me if you have other questions.
PS I don't think you need to hire a copywriter, you're obviously good enough at writing headlines based on how many upvotes this submission has!