I use Corel Draw personally, not cheap and possibly over kill for just eBay listings. I guess it really depends on what exactly you want to design as to what program would best match. Draw Plus is a free download, that may be enough for you to do what you need.
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Btw, if you want to have complete flexibility in your design and do a HTML template, but can't code it yourself. Just yell out and I will put you in touch with someone who will code the design for you for 10 bucks.