It depends on the business, but I have found that finding community forums that have an interest in your niche is a good place for an advert. Email the owner or webmaster and negotiate the rate.
If you are a good fit for the site, the owner and community will love the added benefit. Give a discount and it will be a feature, or value added, benefit to being part of the community, not an annoying advert.
If you are a good fit for the site, the owner and community will love the added benefit. Give a discount and it will be a feature, or value added, benefit to being part of the community, not an annoying advert.