We just released over 10 different banners that our affiliates can use to promote eMiniMalls and refer publishers. Check out the sample 180x150 banner:

The following banner units are also available:
180x160, 120x90, 120x60, 120x240, 125x125, 110x32, 88x31, 80x15 , and 468x60.

Please login to your account and click on the "Referral Program" link to access the customized code for your referral banners.
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Update:

• Added a few more formats. Specifically, 729x90, 300x250, 250x250, 120x600, 160x600 and 160x160.
• The background is now transparent and so can be used on non-white website backgrounds.