An affiliate program is only as good as the creative offered to promote it. By the term creative we are referring to the tools used to promote the products which can be banners, text, emails or any other form of advertising you may find on the internet. A majority of programs still have a preference towards graphical banners (e.g. 468×60’s) as the core means to promote their products. The main exception of course is Google Adsense and the other PPC programs (e.g. Yahoo! Search Marketing or the new Microsoft Adcentre) who are mostly based on textual creative. Google is coming out with more interactive advertising every month however it is our belief this will, in the sort-term at least, continue to be anciliary to the main textual advertisements.
Many programs will have directly in their terms and conditions that you can only use their own adverts to promote their products however this is usually a rule that is broken regularly. A program is not about to turn away revenue from an affiliate if they have spent time creating their own adverts (text or banners) for the product. The only times a program is most likely to use this section of their agreement is if the affiliate is using objectional (or sometimes badly designed) creative.
If the product you’re looking to promote does not have the advertisements you need then the first option would be to develop them yourself. If you would like to stick directly to the terms and conditions (or at least would like to show yourself as a good affiliate) it is a good idea to send the creative to the manager of the affiliate progam for authorisation to use in promoting their product. The secondary option is to request specific styles of creative which suit your promotions from the program itself. This has varying success depending on how much revenue you generate for the program already, who is looking after the program and how much time is dedicated to specific creative.
Overall the key is to use creative that suits your site, not just creative that the affiliate program believes is the best for their product.