1 - 300x250(inline rectangle)
1 - 728x90(leaderboard)
In the ad, I wan't to get across:
1) Who the ad is for i.e., people who shop on Craigslist
2) The benefit of NotifyWire (i.e., saving time and getting to the best deals first) and perhaps some way to illustrate a that benefit by showing (multi location search, image previews, saving searches, search monitoring, SMS and email alerts,etc)
4) The software is Free with an upgrade for Pro users.
Designers may want to try the fully functional free version to get a feel for the software. It runs on Windows, Mac, and Linux. Go to notifywire.com to download. I included some screenshot, but they're not necessarily required for the banner ad.
I'm not married to any particular ad style (cartoon, illustrations, etc...), so please be creative!