At last!  There is now a web site where you can view all of Craigslist & eBay postings together- well, at least for a few categories.  I am a motorcycle and scooter enthusiast, so finding this site was like a slice of heaven to me!  It's a little clunky to look at, but it is functional.

So far, the mashed categories include:

• Bicycles
• Boats
• Instruments
• Merchandise (which as of today consisted of "bowling, pool cue & scuba")
• Motorcycles
• RV
• Vehicles
• Green
  Vehicles
• Vehicle Parts

Here is a link to the site:
http://www.jaxed.com/cgi-bin/ms.cgi?veh=mini+cooper&state=&fil=&ys=&ye=&submit=go

Navigation is fairly straight forward.  Choose your main category from the top navigation bar.  Then, you may browse the available sub categories, by clicking on the blue text links, or you may use the drop down menus located on the top right hand corner of the site.

Enjoy!