Any professional SEO knows that the most effective links for high SERPs are text links. You hear often: it’s better to have a text link pointing at your site than a banner, button or other image link. While for the search engines this is true, for your visitors it doesn’t really matter. A good banner placed on the right website might skyrocket your site revenue by generating more visits from ready to buy customers.
Ideally you should be able to place such banners on sites with high traffic stats (simply check out their Alexa score). But banner space on authority sites is many times overpriced. If you find sites with decent traffic and a topic more or less related to yours that sell inexpensive banner space, you should take advantage of the offer. Ideally the image links should be placed on the landing page of the site linking to you. If such a placement is not possible try to get a position on a related page with a decent PageRank. You should also make sure that the banner is on a highly visible place, like the top of the page or the middle.
To make a long story short: text links bring you that “link juice” your website needs for high SE rankings while image links bring you clicks. People are attracted by images and they are going to click on a banner if you are savvy enough to convey your message into a banner design that appeals to your audience.
When it comes to online marketing use all possible channels to brand your website and your business.