*You want your affiliates to be successful!
If you're paying a lot of commissions to your affiliates, it's because they're out there selling for you. Create a newsletter just for your affiliates and give them useful articles on how to be successful. Profile your super affiliates to inspire others who might just be getting started.
You might consider advertising on some of the sites that are run to support the web sites in affiliate programs. Write articles for those sites as well as other related sites and include a link leading to your affiliate program.