I just read about BannerSketch, a free banner creation website from on MakeUseOf.com.

Bannersketch.com allows you to create a free ad banner by selecting from the most common sizes or defining your own; choose color and gradients;  select frames and text; select fonts.

When finished, Bannersketch will email the finished banner, watermark and branding free!  Sounds like a winner.

Check it out: Bannersketch.com